So lets look at each setting for a hot minute. What specifically is needed for each?
Greyhawk: By virtue of its "default" status in 1e and 3e eras (abet limited) it is the poster child for PHB options. By virtue of the 3e alone it made room for every race but dragonborn (tiefling was in the 3e MM as a monster) and warlock, and nothing about either of them should exclude it from Oerth. By the same token, I can't think of anything NEEDED for them, maybe some backgrounds or a subclass or two?
Krynn: Well, halflings are replaced by kender, but as I've said, that's a subrace. The 5e PHB also hints at a relationship between draconians and dragonborn, so I could see them working as well. Half-orcs are out, but I could see the possiblity of tieflings. As for classes; the 3e Dragonlance book has options for all the 3e PHB classes except paladin, and nothing on the warlock (though the SCAG mentions how to fit both classes in DL, so WotC is willing to allow them). Add on some of the DL races like minotaurs and Irda and then a few subclasses for things like wizards of high-sorcery.
Mystara: Despite its rooting in Basic (when options were limited) I don't see anything in that setting that specifically excludes any options from the PHB (drow replaced by shadow elves, perhaps?)
Aebrynis: I literally no nothing about this setting. Anyone want to chime in on why something should be excluded?
Ravenloft: The Arthaus RL PHB found room for every 3e class and every 3e race but half-orc (the latter refluffed as mutants known as calibans). Warlock certainly fits the feel, and since the Mists take all types, I don't specicifally see excluding tieflings or dragonborn (though I don't expect they'd be exactly welcomed either). In fact, 4e's Domains of Dread Dragon Mag articles described a tiefling domain, IIRC... All that's left is the half-Vistani race and a few subclasses or backgrounds to represent knights of the Circle, Avengers, Anchorites, and such.
Eberron: Everything already has room for everything. All you need is the artificer class and warforged, shifters, changlings, and kalashtar (the latter needs the Mystic as well.
Planescape: The definition of "everything". Add Rogue modrons, githzerai, and bariaurs.
Kara-Tur/OA: Well, the 3e OA book removed paladins, clerics, druids, bards, wizards and replaced them with oriental variants. I don't see WotC going that route this time, I more fully expect some of the classes will just receive Asian-inspired subclasses (a shaman/shugenja domain, a sohei, a ninja, a samurai, etc). Pathfinder has done a great job with this sort of "reusing/refluffing/variant" model. As for races; while Kara-Tur doesn't have much contact with elves and dwarves, it IS part of Faerun and thus could have some "gujin" races if it wants, but I'm alright with having the OA races take center stage here.
Athas: If we take every version of DS from 2-4 and average them, we get Barbarian (2), Bard/caster (2), Cleric (2), Druid (3), Fighter (3), Monk (2), Paladin (1), Ranger (3), Rogue (3), Sorcerer (2), Warlock (1), and Wizard (3). So Paladin and Warlock have the least clout, though WotC might save warlock due to the ease of making a Templar Pact vs a whole Templar class. So Paladin might be the only casualty? You will probably want to replace a few subclasses with more Athasian options as well. As for races; you need Athasian subraces for dwarves, elves, and halflings, no gnomes or half-orcs, and then room for half-elves, tieflings, and dray/dragonborn. Add Thri-kreen, Muls, and Aarakroca, and then Mystics for psionics and your done.