Surprised not to see any commentary on Spelljammer or Planescape; what do folks think these settings need?
Despite the fact that these are big parts of my game, I didn't mention them because I think they are both a combination of setting and meta-setting.
Since we get a lot of planar stuff outside of specific setting material, we don't need that repeated. I'm also not mentioning anything that is known to be included in upcoming products (such as githzerai and githyanki). What we do need is this:
Planescape
Races:
-
Maybe rogue modron. (It's fringe enough it isn't essential).
Monsters:
-More planar exemplars. Archons, guardinals, eladrin -- the original recipe, not the 4e appropriations of the name. Gehreleths, heirarchy modrons, probably others
-Dabus and other Sigil/Outlands iconics
-Lots of others probably
We do need some way to represent special powers from the factions, but it's difficult to balance. The best way I have thought of (and what I'm using in my game) is to make faction membership a new character Bond. As long as you don't totally disregard your faction philosophy, you get a magical benefit(s) and a magical hindrance. The benefit(s) should slightly outweight the hindrances, but not by much since you don't have to pay any build resource to get this feature.
As an example, for the Society of Sensation, you write a Bond that fits, and get:
-Darkvision 30 ft. (or your darkvision range increased by 30 ft. if you already have it)
-Advantage on Wisdom (Perception) checks (including Passive) to avoid being surprised by an ambush
-Disadvantage on saving throws against spells that attempt to overwhelm you through your senses (stuff like
hypnotic pattern--there aren't a whole lot of these, but if you count Xanathar's, probably a dozen or so)
For planes, I don't think we need a lot of mechanical effects--and the ones in the DMG need to be seriously downgraded in power. I'd change all the "after a long rest" ones to "each month", and say that they are negated in specific settlements or regions that are intended to be visitor friendly. Or make them weekly instead of monthly, but include planar keys that you can keep on your person that make you immune to the effects. That's all more complicated than I'd like, but we need a way to both have effects, but let merchants and travelers actually go to these places and stay at inns without transforming overnight.
We absolutely don't need any of the stuff where spells get a +/- modifier, or X spells don't work, etc. That's all AD&D design--even 3e simplified it. 5e ignores it entirely. What we
could have would be sections that suggest some of the less mechanical but awesome features of the planes. For instance, how if you don't do good deeds you can't get where you want to go in Elysium, or how you have to stay on the roads to get anywhere in Arcadia, or even how (as a slight exception to my previous point) you can't use non-natural flight in the Beastlands. Cool stuff like that that is more fluff of a weird locale than mechanical stuff.
Spelljammer
Races:
-Probably a couple, but not many
Monsters:
-Here we need a
lot
We also need spelljamming and arcane space rules. They need to be simplified, non-punitive, and consistent. For example, clerics cast spells normally, but only some faiths have a presence in faith. There needs to be a balance of keeping the flavor without making the rules a hassle. For instance, I'd almost say they should just say that wildspace and the Phlogiston are filled with a breathable "air-like" substance so we don't have to worry about air. That's iffy though. The rules for helms need simplification, and you shouldn't be out of action for the day once you strap into the seat.
Note that in contrast to the other settings I talked about, I didn't mention any classes or subclasses. That is intentional, since neither of these settings need anything of the sort. I don't even think they really need subraces. Maybe a lizardman subrace (we already have the race in Volo's Guide) to better represent the spacefaring version.