Defilers/Preservers: if you don't take preserver feats, you start to lose your party's rations of food and water?
Clerics: keep in mind that the ultimate cosmology is going to be based on the Axis. Dark Sun was still in the Material Plane and thus in the Great Wheel; just cut off from everything. Getting through the Gray to the Elements (in this case Elemental Chaos) is going to be only slightly easier than going anywhere near the Outer Planes.
I expect Primordial elemental personas of some sort for elemental clerics. I expect Templars, if a PC class at all, will have one Unaligned Sorcerer King to choose from for their spells; I expect this means the Democracy city-state is going to be that way, unlike the original boxed set (or not; they said the Pentad was going to be an option for how things could-have happened).
Survival Checks: everyone will have this as a bonus skill. You have to roll for each set of abilities during an extended rest, to see if you get them back. (that sounds awful, though, so I doubt it)
At the very least, you have to roll to avoid a penalty to your actions; IF you don't have food or water, that is.
They'll have Mounts for travel, as that's such a huge part of things. Encounter guidelines for trade caravans, walking, and floating.
Environmental rules are obvious, from hazards like the silt sea, to the Ringing Mountains (penalties to breathing air).
Psionic feats are likely. I doubt everyone will get a bonus feat, but they'll have Psionic Talent-style background options, as well as Feat options, to choose from.
Races: I am fairly certain they'll have a different breed of elves for this. Or feats to boost running speed. I'd be surprised about Feywild races, as I think gnomes were eradicated. Read it in Wikipedia today

Dragonborn are a shoe in, and would fit the setting. Genasi would also fit right in, as would Goliaths, Githyanki, Minotaurs, shifters, half-orcs, and even Deva (angels who avoided destruction by taking flesh form?).
Extraplanar races like Feywild ones may well have a region in the world they can come from. Also, Athasian Underdark info would be of interest (allowing options for individual campaigns without saying specifically what goes there).
expect Dragon articles on how to fit in races from other settings (warforged found in some ruin, etc.)
Likely there will be guidelines for having more in the setting than before, but focus will be on classic elements rather than cutting things out. They just won't mention stuff, I guess. Not kitchen sink, of course, but why state limitations? Banning it outright own't happen per se, as you could always find something from ages past in some ruin or other. They will just say that stuff like that is uncommon, and someone will try to rob you.
I think rules changes to the setting will be added to give more bang for your buck: I don't pay money to have my PC die. I want a challenge, but I want to see the end of the module, for example.
That said, how to make the PCs' lives miserable, but the player experience FUN is going to be important. I expect a rewards system for XP during survival checks (even for failing; the die failed, not you), in case the PC you like gets hurt. Or action points handed out when you're beat up badly.
I don't think scheduling my week around a game where the DM is going to tell me that my PC has died for no good reason, based on a roll that I have no control over, is worth the money, time, effort or aggravation. If you do... well, there are fine places you can go for a good spanking. I highly doubt WOTC wants to be that place.
You go for excitement; you keep coming back for that; they'll make a Dark Sun you'll want to come back to.
The trick to the rules changes is making harsh environments and shattering weapons... FUN. The fans WANT the harsh. but it has to be fun, and it has to be foolproof (in case my DM sucks).