Interesting! Feasible?
1. Don't need this, wouldn't work with my cosmos, nor likely work with many homebrews, and take to much effort on WotC part to be worth it.
In regard to an actual map of the D&D Multiverse "not working with your cosmos, nor with many homebrews"...the same could be said for a map of any land, continent, or world...whether it be Faerun, Toril, Oerth, or anything. Any DM who's worked with those worlds will have developed divergent stories and lands. That shouldn't stop WotC from trying to gather all existing published info about those lands and worlds, or stop them from publishing a complete map of Faerun, Toril, or Oerth for 5E. The same applies to the D&D Multiverse.
But if you're assuming that I'm talking about shoehorning it all into the Great Wheel (instead of depicting world-specific cosmologies, such as the Great Tree and Eberron Orrery), that's not necessarily the case. I see though that for 5E (so far) WotC has decided to depict the Multiversal map as a mix between the Great Wheel and World Axis, and I assume that will continue to be the case in any 5E Planejammer setting, with the World Tree and Orrey (and other world-specific cosmologies) being explained as just another way to map the connections between planes and planar dominions. But I say that in order to be a complete map, the usual 5E planar map, would also need to include inset maps or supplementary maps (on another page) which show how each of the major world views the planar map: Toril's World Tree, Eberron's Orrery, Mystara's Five Spheres, etc.
As for such a "planejammer" map taking a long time to figure out...much of the work has already been done. Paul Westermeyer has gathered all official references to Spelljammer routes, and has mapped them out in
"An 'Official' Guide to the Spheres" - the map is on page 6. So just take Westermeyer's map, and merge it with a more detailed version of the 5E Planes of Existence map, add in all of the obscure worlds and planes, have an artist beautifully render it, and voila!
As for a full planetary map for each of the major worlds, I've gathered a bunch of them in my
Atlas of the D&D Multiverse. Many of the worlds have full planetary maps, at least with bare continental outlines: Oerth, Abeir-Toril, Krynn, Eberron, Mystara. For the other worlds, I'd advise WotC to not worry too much about areas of a globe which haven't been depicted at all. Just show the existing mapped areas as more detailed, and sketch in some continents on the rest of the globe and call it done.
3. Interesting idea, could include rules but as for the rest see #1.
Much of the work of correlating timelines has already been done.
Temporal Chronology of the Primes:
https://web.archive.org/web/20110711...chronology.htm
Spelljammer Timeline:
http://www.spelljammer.org/essays/hi..._timeline.html
Unified Multiversal Timeline:
http://planejammerchronicles.com/about-2/
Timaresh's Timeline:
http://www.rilmani.org/timaresh/Timeline
Timeline Converter:
https://web.archive.org/web/20040720...nd/chrono.html
Also relevant is TSR's "Chronomancy and the Multiverse" (RTF download) which notionally includes (though without dates) many worlds within the D&D Multiverse, including such obscure worlds as Historical Reference Campaign & Masque of the Red Death (D&D Earth), Gamma World, and Council of Wyrms.
http://www.enworld.org/forum/showthread.php?358019-Grand-History-of-the-Multiverse#ixzz3AxZFuIWd
FR recent events (5E adventures):
http://www.forum.candlekeep.com/topic.asp?TOPIC_ID=19630
Mystara is one key world which hasn't been clearly synchronized with the other timelines.
Here are the known crossovers between Mystara and the other worlds:
http://pandius.com/mystchar.html
(I'd add to this list the world-gates which were mentioned in the AD&D conversion guide in the back of some of the Gazetteers and connect Mystara with Greyhawk and Forgotten Realms. And also the world-gates from the Book of Marvelous Magic, which connect Mystara to Greyhawk, Dawn Patrol, Boot Hill, Gangbusters, and other early settings.)
Here's one enthusiast's attempt:
http://www.thepiazza.org.uk/bb/viewt...133501#p133501
And discussion of details here:
http://www.thepiazza.org.uk/bb/viewtopic.php?f=3&t=3223
The discussion includes future events, such as correlations with the Greyhawk 2000 "D&D Modern" setting.
For reference, here's the existing Mystara timeline:
http://pandius.com/timeline.html
A discussion of whether all the worlds advanced 100+ years for 4E and 5E. Includes info about Elsir Vale from 3E Red Hand of Doom which exists in 4E Nerath:
http://www.thepiazza.org.uk/bb/viewtopic.php?f=4&t=15942
As for "game edition" Realities, I'm the only one (that I know of) in all of D&D fandom who has really worked on that concept. It's a forgotten but useful tool for wrapping my mind around the different rules-based depictions of the same world. WotC is welcome to use my research:
https://sites.google.com/site/dndphilmont/d-d-realities
https://sites.google.com/site/dndphilmont/realities-and-worlds-chart
https://sites.google.com/site/dndphilmont/continuities
5. See #1, besides, I prefer to decide whats connecting or not.
Even if WotC connected it all, of course, anyone can decide what's connected in their campaign. There's no question about that.
As for including an official mention of the wider Hasbro "Megaverse", I'm proposing only a brief paragraph. And I'd keep the non-D&D IPs as distinct "multiverses", which only lightly and rarely (and optionally) connect to the D&D Multiverse. But c'mon, it'd be cool to have a D&D/Transformers crossover. And...as others have said, it is likely that there will be more M:tG D&D products...presumably M:tG may soon have in-world connections with D&D. I'm offering a deft way of connecting the D&D Multiverse and M:tG Multiverse...in a very loosely (and optionally) connected Megaverse. I mean, another Hasbro department (Transformers) already officially uses that term "Megaverse" to distinguish cross-overs (with GI Joe etc) from the Transformers Multiverse.
Overall your ideas are interesting, but I dont think they are feasible.
Thanks! We'll see! Will never happen if no one voices it.