For the planes at the moment I'm using the planes of Zeitgeist as shadow demiplanes in Khyber as described in Exploring Eberron by Keith Baker. Each demiplane has a link to the normal planes in the Ring of Syberis. As such the sealing of these demiplanes has been done by the Gatekeeper rituals in the past. Further reading of the adventures might change this though.
The plan of the Obscurati is to replace key planes with alternates, based on the premise that to work properly, the material plane must "get" something from the 8 linked planes : fire, air, water, earth, space, time, life and death. Each linked plane also provide smaller traits. So the flight restriction is a small trait of the plane of air, gold blocking teleportation comes from the plane of earth as "minor qualities". Players will get the opportunity to get acquainted with other planes providing other qualities and maybe select some other choice than the original ones. It could be explored more in depth than in the campaign if your players "dig" into the metaphysics and start asking questions... and it's something that doesn't fit the 13 planes system of Eberron. You will have to take that into account. Either by removing the part where the players are presented with another choice than the original, gatekeeper-approved setup [and it could be very valid to have the dragons explain that "if the people of Khorvaire modify the design of the gatekeeper, we will squat the people of Khorvaire like we did with the giants"... but I feel it will remove an important piece of the ending where the heroes are really empowered to change the very foundation of the world. In this case, you can gloss over the details, present the attempts of the obscuraty as misguided meddling and just have the players restore the original design. If you expect your players to like the idea, you will have a lot of work to modify the ending. Even the Ob doesn't need to change everything, so they can have the intention to modify only a subset of the 13 planes. But you still need to have the planes provinding "something" and the Eberron planes aren't aligned neatly on the 4 elements and 4 energy of Zeitgeist. Creativity is called.
You're planning to have the planes as demiplanes of Khyber... It's a good idea but it downplays the "world defining impact" of the planes. It might sound strange that fundamental world-building qualities are provided by Khyberian demi-planes while the original planes only have muted consequences, mostly appearing in key manifest zones.
If you want to map, t's easy to have Irian and Mabar as life and death, the 4 elements aren't really represented... because the four elements are embodied by Lammania. Planes of Eberron, according to Exploring Eberron, seems more linked to the sentiments of the living : Risia isn't the element of ice, but "isolation, preservation, stagnation". In some way, the Eberron planes provide something but more affecting the lives of the people than the building block of reality. I have opted (but I don't know yet how it will play out, my players aren't this far) to do some extensive rewrite to the Ob ritual, saying that
1. the arc of Syberis initially encircled the 13 planes and where supposed to interact freely so it's the Original Design (but lost).
2. each plane was providing energies necesssary for the material plane to work properly... if you don't have them all, you have the Gyre consuming the world, because of low energy to maintain reality.
3. each plane also provide the moral elements as explained in Exploring Eberron. I won't paraphrase what it's in there, but Fernia isn't the plane of fire, it's the plane of destruction and industry. In my game I have pointed out that Fernia has been close to Eberron over the last 100 year, which corresponds to the Last War and the many invention (magitech flight, warforged...) or that Dolurrh provides the idea that "souls fade to nothingness after death"... Hinting at this during the campaign and that Fernia isn't "just the plane of fire with a fancy name" is making it possible for the players to ponder the consequences of their choices in the end...
"So you want to replace Fernia ? OK, you can, you have many alternative... but maybe you'll make technological progress impossible ever... You don't like Daanvi? Remove it, but say goodbye to justice and social organization spanning more than a hamlet... so you'd better be sure that the trait "water is healing and most people recover overnight" or "the world obeys newtonian laws" is worth it to you.
4. The giants cast Dal Quor away, sealing it off, but they didn't remove it. So it is still providing individual dreams and aspiration... but dreams can't become true easily as they could before, therefore there is no more "heroes" [except the PCs], a foundation of Eberron.
5. The dragons didn't like the giant intervention and wiped them and replaced a plane (now forgotten) with Kithri, the constant change, to make sure than no civilization can last long enough to rediscover the secrets of magic able to shatter the world [hence the Xendrik curse and the collapse of Galifar]
6. The Gatekeepers sealed off Xoriat but kept it as an energy source in the ritual. It's difficult to get inspiration and great artists are rares because of that [and the invasion by Daelkyr was stopped, so maybe the trade-off was good enough: I made sure the players get this information to get the idea that not all meddling is necessarily bad...)
The Obs are divided into factions and a fun part of the campaign will involve discovering their plans... My decision was to keep the goal of each faction, "keep" the new planes they are pushing into the system and suggest they just replace planes they don't feel needed to "make way" for their choice of planes. So the Arboretum wants to control nature for the greater good? OK, they will need to remove Kithri (constant change is bad) and Lamannia (nature is wild and untamable) by to planes of their own. And so on. If your players express some preferences, they will have the opportunity to be active players in the grand finale, especially as they will have the opportunity to "find" planes in the Gyre in the latter part of the campaign. If your players dig this part, it's worth thinking about it much earlier because questions will arise during the campaign, and probably earlier than expect. I notice you got rid of the "limited flight" aspect of the Zeitgeist setting, I'd even go all the way and have Syrania gives the trait "flight is easy, things don't fall like they should" explaining Sharn. So basically, if someone wants to "make room" for a plane of their choice, the consequences of removing Syrania would be long-term (less trade... it might not be very bad) and short term (architectural collapse of the largest world metropolis). I'd advise imagining consequences both good and bad of removing each of the 13 Eberron planes in case players asks questions and love this aspect of the endgame (I can provide my list later). From what I have read in threads of actual play, interest is usually high. If you just remove the third part of the campaign, you won't have to think about it, but I feel it's a loss. The Zeitgeist ending is truly a masterpiece fitting level 20 characters, something very few AP can achieve (nearly none, actually).
In my conversion there will be in alliance between the Fey Titans and the royal family of Aundair. This pact is probably from the start of the Last War, but it could be older. The Fey Titans will rise up to Aundair either in defense of the Eldeen Reaches or too much industrialisation in Aundair.
By the time they rise up, the world is in such a sorry state anyway that industrialization isn't a major problem. By the time of adventure 10, magic has become wonky, the sun has been turned off, planes are being dragged into a churning chaos in the sky and hiveminds are taking over the thoughts of sentient beings. I think windmills will be quite low on the list of concerns. Defending their "natural domain" in the Eldeen Reaches will undoubtably feel better.
I agree with two dragons in disguise is too much for Eberron. The minister of magic in Aundair is the brother of queen Aurala and Pemberton is not really fitting for dragon behaviour in Eberron. So maybe no dragons in disguise? The brother of the queen could be replaced by a dragon of the Chamber, because they know something important for the world is going to happen in Aundair and they want first hand knowledge.
I went with no dragons in disguise. Especially since I made dragons the origin of the ritual to fit Eberron lore, it wouldn't be convenient to have two dragons available to provide information. If the players want information, they are free to travel to Argonessen (from which no one has ever returned, so it won't be the easy way out).
I've started reading in the 6th adventure and I was thinking about making Pemberton a rakshasha allied to the Overlord of War (Rak Tulkhesh), a higher member of the Lords of Dust, maybe even Mordakhesh himself. I know the minotaurs in Droaam are servants to Rak Tulkhesh, and I think the gnolls not in the Znir Pact are also servants of Rak Tulkhesh.
I can see it working: Pemberton would try to jumpstart another war involving Droaam because the draconic prophecy connects it to the release of the Overlord. It didn't work during the Last War because there was no Droaam as an independant player, so they are trying to correct the problem to see if they can enact the prophecy. But... wouldn't the Overlords SIDE with the Ob or try to influence it to a planar arrangement that would free them? If you make the minister of magic a Chamber dragon, and the goal of the dragons is to preserve the statu quo, then the goal of the Overlords would be to disrupt it. Unless you remove dragon involvement altogether and the minister of magic is just the regular brother of Aurala.
I do like your idea of making Pemberton an important member of Cannith South. This might increase the struggles with Cannith West in Aundair. I have to think about this and read further in the adventures before making a decision.
Yes, because Cannith South + a Droaam army + access to a forge of creation (nothing in Thronehold prevents forge of creation to be created on another plane of existence) = instant win for becoming the patriarch. Legitimately, Cannith West would want to stop this effort. He'd be operating in Aundair because it's the only place where the Dolurrh manifest zone allows transit to his creation forge, and relying on criminals for his materials because (a) he doesn't want the project to be linked to House Cannith too early [even if it's TECHNICALLY LEGAL, it's better to keep a low profile] (b) he doesn't really trust the Colossus ordered by the Obscurati but they provided invaluable help to fund the rebuilding of a creation forge so he didn't have to draw on Cannith funds and expose himself to an audit. So he's partly rolling with us in the beginning, then trying to consolidate his power base, but still spying on the Obs because he's not sure what they will do and finally siding with the PCs when he realize that the threat of destruction is too high. Deciding on his exact role will be easier when you have read further ahead.
Which cities did you use for the lightning rail route in adventure 4? I'm thinking about starting in Sharn and ending in Thaliost (adding a track to the map between Flamekeep and Thaliost). The biggest issue I have is with Nalaam. As written this would not be a city in Thrane. I'll make it a special line that stops each night which normally is not the case for the lightning rail. Normal stops would be: Sharn, Wroat, Starilaskur, Vathirond, Aruldusk, Sigilstar, Flamekeep, Daskaran, and finally Thaliost. The second issue is the long distance between Wroat and Starilaskur. How did you solve these issues?
KB has in an IFAQ about transportation supported the idea of several stops "not on the map" and even LINES not on the map, as if the cities mentionned along the rail route are the one "express trains" stops at, with the possibility of many local trains having a much more leisurely pace, including stops. The outrageous cost of the lightning rail (compared to the wages in Eberron, making it difficult to have anything other than uberfirst class to be realistic] is only for the most express route, and many more options exist. Because adventure 4 feature a voyage long enough for the lightning rail to cross the whole of Khorvaire... In my Eberron, only higher dragonmarks allows operating the lightning rail for long shifts, and therefore the lines on the map are operated as is on the most costly lightning rails only. Most rail activity is operated on shorter shift, with regular dragonmarked conductors, who needs a long rest and a good night's sleep.
I solved it by having the stops be Sharn, First Tower (military garrison being changed, this is a mandatory stop even if it's very close to Sharn and Wroat, and regular passengers are expected to stay in the Orien enclave) as Keskay (Eleanor is on her business trip with high ranking officers, Oliver Boone and Verzubak have background that would fit being in First Tower and not travelling in coach with the soldiers and I moved the racist incident with the Grietnos one station early as it was more fitting for a border garrison town to have disgruntled soldiers acting this way), Wroat as Cherage, Orithea as Orithea, which I decided was a town south of the dragonwoods, Trekholm as Hatheril (in my Eberron, the rail line goes to Hatheril, where part of the train continues on to the north toward passage, and the rest of the train continues eastward, it's more economical than having two separate trains). For you, it's also a close stop to Aundair, so it will be convenient to have the supply ship, converted to a supply support group, meeting there in a border town), non-eventful stops in Starilaskur was mentionned in passing, Nalaam as Sterngate border station. (Technically Sterngate is Brelish, but wouldn't you want the train to stop right at the zil border? I found that the idea of using criminal as workforce was very Zil and especially The Trust, and it was however far enough from Korranberg to be a den of villainy (near the disorderly brelish, you see) Sid Minos as Zolanberg and finally the Korranberg terminus.
On adventure 4, my main caveat would be "pray that the PCs actually don't think the travel is just a short diversion (and don't forget to make that clear)". Because if they think the important part will be the information they will get at the end of the trip, hoping to infiltrate the Ob by following the other leaders, they will be disappointed. And if they hop on the rail thinking that, they will not "buy" all the interesting things happening on the trip.
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