I think we will never get a setting which does not allow PHB material.
Everything WotC is doing nowadays is herding its player base together using a "D&D setting". This is necessary to finally break out into the really profitable markets: movies and their merchandize. To Hasbro, ttrpgs is a minute sideshow.
I consider this option wholly divorced from reality. During this edition's run WotC has done everything it can to not split their player base like that.
Here is the thing: Dark Sun is a setting that proudly spit in the eye of the medieval fantasy setting presented in the normal PHB. That's it's selling point to many. Talk to a Dark Sun player about what races and classes shouldn't be allowed in the setting, and you'll get on average 50-75% of the PHB options as not compatible with the setting. Even though WotC included material in later DS for 3.5 (Dragon Mag) and 4e, there is a part of DS's base that would riot at tieflings, paladins, monks, half-orcs, and the like on Athas, let alone hill dwarves and wood elves.
They have said, often in relation to psionics, they are working on Dark Sun. They have only a few ways they can do this:
1. Sell a setting book that tells it's players a sizable chunk of thier other books can't be used;
2. Create a version of Athas more accommodating to the PHB, at the cost of some of its identity;
3. Create a separate spin-off game, akin to Gamma World, that is compatible with 5e but uses is own version of the 5e engine and can alter whatever is needed to fit the settings aesthetic.
1 can never fly for today's WotC; they are not about telling players and DMs what is/isn't allowed. So 2 and 3 are the only reasonable options and the choice between the two comes down to what is more important; PHB compatibly or setting purity.