The Irony of 5E's Campaign Setting Releases

In theory, all the D&D settings take place within the same multiverse.

The "Great Wheel" cosmology places worlds like Oerth (Greyhawk), Krynn (Dragonlance), and Toril (Forgotten Realms) all in the same Prime Material Plane, separated into different "cosmic spheres" but still ultimately in the same physical reality. That means each of them is also affected by the various other planes - the Feywild and Shadowfell, and the Outer Planes like Limbo, Mechanus, the Abyss, and Mount Celestia.

Ironically, however, the two official Campaign Setting books that have come out for 5th Edition do not fit within that same cosmos.

First off: Ravnica's exceptionalism is to be expected - created originally (and continuing as) a setting for Magic: the Gathering, Ravnica naturally has to be tied to the whole Magic multiverse (which used to be canonically called "Dominia," but that's a term they probably haven't used in twenty years. The primary plane in Magic, Dominaria, is "Song of Dominia" because it was at the center of that multiverse.)

Given the, I think, canonicity of the Acquisitions Incorporated games, it would seem that it is, technically, possible to travel from the Great Wheel cosmos to the Magic multiverse, but requires crossing the Far Realm (something I did to allow my friend's level 18 half-orc sorcerer to get there for a one-shot.)

The Far Realm, in fact, works pretty well as a catch-all to link fictional universes. Because it is essentially "outside the outside," you could argue that the Far Realm is just one name for the most alien place imaginable. Indeed, my own D&D setting is technically in its own pocket away from the Great Wheel (largely because I wanted to make up my own outer planes.)

Eberron is in an odd position, though.

Created at a time when there was not the same desire to link all D&D setting together in this way, Eberron has its own planes, which work very differently than the Great Wheel. They aren't linked to alignment in the same way, and elemental planes are not all that distinct from the planes of fiends and celestials.

Eberron is, of course, one of the most popular D&D settings, but it does strike me as kind of funny that they've only done two non-Forgotten Realms setting books and neither has the same cosmology as FR.

Personally, I'd like to see something very outlandish for the next 5E setting book (which, you know, take your time - Rising from the Last War just came out two days ago.) I'm hoping for Ravenloft, Spelljammer, or Planescape, none of which take place in the Prime Material Plane.

Still, particularly if it is Spelljammer, I do wonder if we'll get some fleshing-out of rules on how to travel from one of these setting to another. In theory, I believe just normal physical teleportation allows you to go from one world in the Prime Material to another, but given that Eberron is isolated thanks to the Dragon Above and Ravnica's in a whole other multiverse, I wonder if you could really do a 5th Edition Spelljammer setting yet. Yes, Ghosts of Saltmarsh technically took us to Greyhawk, but that was certainly not a full campaign setting book.