Zardnaar
Legend
I get WotC wants to "take it slow" but dammit a toe in water conversion for some of the races, major monsters, and such for the major worlds would be nice. Official "we visit this world in X sup or Y AP" is great for 5+ years down the road, but a few of us just want official warforged stats!
That said, I have a personal theory that when WotC does visit other worlds, you're going to see two design philosophies going forward.
* Each world is going to have a "hook" that can be described in a sentence; "Eberron is pulp/noir exploration and magitech", "Dragonlance is chivalric knights and wizards vs. evil dragons", "Greyhawk is sword-and-sorcery adventure in a morally gray world", etc. Each world will present a clear "theme" or "reason to exist" beyond "Its not Faerun."
* The world will, to the best of their ability, try to retain as much of the Player's Handbook "default" as possible. That is, alternate rules will be played down and the majority of "additions" will end up being races (kender, mul, shifter), subclasses (wizard of high sorcery, gladiator) or backgrounds ("dragonmarked heir, Templar). I also expect few subtractive rules in an attempt to keep the "core" as true as possible (All halflings in Dragonlance use the kender subrace...) so expect dragonborn on Oerth, tieflings on Krynn, and Clerics on Athas.
My theories are mostly based around how Ravenloft was handled in Curse of Strahd; they could have opted for a number of Ravenloft-era rules (spell changes, fear/horror/madness, Power checks) but instead did the minimum (a few cosmetic spell changes beyond the planar travel ban and Resurrection). Hell, they didn't even to re-invent some of them; Fear and Horror are in the 5e DMG! They did it so as to make the game work without much additional info, and I feel they're going to try to do the same with other settings. So I wager that 5e Dragonlance is going to figure out some way of making every PHB class available, 5e Planescape is going to treat the factions like the AL factions, etc.
I know the purists will shriek in rage and horror, but I think when they do move beyond Faerun (and a toe-dip in Ravenloft) that it will error more towards "D&D, with added flavor" rather than "radical rebuild/variant of the D&D system".
Erm Athas had Clerics it was the lame 4E conversion that removed them. They were quite important in the original setting.