the level of screwup is in the eye of the beholder. If nothing but a carbon copy will do, that is on (general) you.
I am sure there are people that think they screwed up DL or Planescape, just like there are ones that do not think so. The same will be true here.
I think they could stick the landing well enough, but it is not guaranteed
I mean, it's an official WotC D&D book.
An awful lot of people will defend whatever they do, no matter how bad. So far we've no bottom limit to what will be defended in an official WotC D&D book (but see later in the next paragraph!). We've seen that at great length. The very worst, weakest, least-well-designed, least well-executed 5E materials get like 4/5 from a lot of people (including most "reviewers"), usually some kind of caveat that there's a "limited audience" or the like lol but still (maybe 3.5 if they're feeling really spicy), whereas the best official WotC products, the highest-effort, most thorough, most extremely well-put-together often just get like 4.5/5.
This is the big challenge that's unique to 5E - it wasn't a thing in 2/3/4E (nor early 5E actually, it only came in after 5E went big) - you just can't even slightly trust reviews because 5E has a sort of... people call it "toxic positivity", but that's not right... because it's not that, I've seen that, that's different. It's like you're required to act like ever WotC product is at least good, or else people just tune you out. And that's the dominant force. There is a small element of justification to this too, because WotC hasn't put out any real like, 1/5 or less products for 5E that I'm aware of (unlike some 3PPs)! They've never made anything completely worthless, just a lot of things that were half-arsed, clearly damaged by arbitrary seeming format decisions (i.e. the 3-book in a slipcover insanity), artistically very empty and and sometimes not very well put-together mechanically (thought still better than many 3PPs of course in the latter).
Now, there are people who are also very negative about D&D, but it's not at a diametrically opposed angle. They don't just give every product a review of 0.5 to 1.5/5, no. Instead just dismiss everything in cynical ways (some of which are, unfortunately, somewhat justified, given the aforementioned semi-frequent artistic emptiness/phoning it in and format insanity).
Combine this together and you get a tricky situation, because discussion often tends to be between the needlessly defensive and the aggressively cynical, with neither side necessarily particularly interested in accurate criticism lol.
The reality is, they could put out a totally generic fantasy setting, that loses absolutely everything about Dark Sun thematically and tonally and in terms of ideas, except that it's desert survival and technically some (but probably not all) of the main bad guys are Sorcerer-Kings, and which also was say, too short, and mostly a mediocre adventure and bestiary, and a lot of people would still rate it 4/5 and say "I liked it!".
But it'll be disappointing if they do.
I suspect the actual decision-maker to do Dark Sun here is that, regardless of whether it's no-ideas/themes rubbish, it's going to sell a lot of copies. Because most people buying 5E material are under like 30-35 at the outside (according to WotC's surveys), and most of them have never played Dark Sun, so the only things they really know about it are that it was really cool, and had certain things in it - the tone and themes tend to be discussed less than other elements (something sadly true of pretty much all settings in pretty much all games). Anyway point is, WotC don't actually need to go a good job to move a lot of copies here. The question is really if they want to change direction more towards an actually-broader take on what can be in 5E D&D (which ironically, a semi-accurate Dark Sun would represent), or whether the quest for blandness continues or even worsens.
EDIT - My expectation is that they screw it up LESS than a lot of people are expecting them to, don't actually make it generic or too light, do keep Sorcerer-Kings as the main bad guys, do have a lot of suggested restrictions, maybe even have the cojones to default-ban clerics, but that they make some kind of sensible-seeming but profoundly point-missing major lore change (most likely "All Preservers are Druids, All Defilers are Sorcerers" based on current very limited info) that leads a sort of cascade effect through the setting to just make things less exciting/compelling, and we get a lot of Gen Z and very young Millennials going "This was the setting the olds were saying was so cool? Seems ok but not really that exciting to me! Also where is X theme they mentioned?".
