The point of preserving magic was that it didn't defile. Thereby preserving the plan life that already exists instead of killing it. Restoring plant life to athas was usually the domain of the druids. However, preservers did get specific spells that restored plant life as well.
The fact that the defiling sorcerer subclass released in the UA doesn't even kill plants at all, is a swing and a miss.
they both were misses, the preserver did not actually preserve anything, they basically cast an illusion that lasted for a short while and then everything reset to normal. If I wanted to actually preserve nature, this is the last thing I would do. Literally anything I would try to help the environment would have more impact.
And they obviously both fail by making this subclasses when really any use of magic should defile or preserve. If I can just avoid the whole thing by picking any subclass from the PHB, the approach has failed completely. This appears to be so fundamental that WotC should be aware of it too, guess we will see.
The 4e Dark Sun book had one really good list of 8 characteristics of Athas that make dark sun unique.
1. The world is a desert: Easy enough to do with any RPG.
2. The World is Savage: Not sure WotC will be able to support any of this one. WotC won't even print the word "savage" in a book, let alone add slavery.
3. Metal is scarce: Easy enough to do with any RPG.
4. Arcane magic defiles the world: WotC already has this one wrong.
5. Sorcerer-kings rule the city-states: Easy enough to do with any RPG.
6. The gods are silent: Have yet to see anything on elemental clerics in UA. 4e was able to do it using themes, but I doubt WotC will even try.
7. Fierce monsters roam the world: Easy enough to do with any RPG.
8. Familiar races aren't what you expect: I fully expect goliaths to stand in for half-giants (its still a cop-out), but muls and cannibal halflings will definitely get the axe, and elves being portrayed as nomadic raiders, peddlers, and thieves could even be phased out.
I'll focus on the ones you think WotC cannot achieve
2, They still have slavery in other books, I do not believe they have to remove it from DS, they probably will downplay it though. That and and many of the other items reinforce a savage world.
4, yes, the UA got that wrong on a fundamental level, I withhold judgement until the finished product is out however
6. a refluff gets you most of the way there, good enough to leave it at that instead of coming up with new cleric subclasses
8. no idea about muls, let's just assume you are correct. It does not take cannibal halflings for the races to be different from what you expect, they can be different from what you expect and not be identical to the DS of 2e. That would make them truly different from what you expect
My main concern is your number 4, the rest will be a matter of what they actually do with the fluff, but getting defiling and preserving wrong would be a fundamental problem to me