I think WotC should do a Request for Proposal (publicly or behind the scenes) for submissions how a writer/studio would approach Dark Sun with modern sensibilities. If they find the right partner, they license it (with approval rights) but not under the WotC banner (to avoid implicating their brand). Seems like a win-win to me.
Or they could just simply open Dark Sun on DMsGuild. They've already done this for Al-Qadim after all, and Al-Qadim has slavery as a significant setting element (via the mamluks etc), although it's not nearly so central as it is in Dark Sun. This approach would have the benefit for WotC of specifically not requiring them to endorse any single DS licencee, and being able to disclaim and/or yank any interpretation of the setting they didn't like.
Folks who want Dark Sun should start looking at the non-WotC alternatives, of which there are at least a few. I seem to recall one on Kickstarter last year.
I think I remember the campaign you're talking about. It disappeared off kickstarter so abruptly that most people suspect a C&D was issued by WotC, which is quite possible considering how transparent a rip-off of Dark Sun the whole thing was. And from what I saw of it, it absolutely failed to update the setting to modern standards in any meaningful way, and it made me cringe in several places.
Maybe the hinted at forced breeding?
But really, that's such a minor setting element that it could be retconned out of existence and hardly anyone would notice, I suspect.
No, the main issue would be how to portray slavery, with a side-order of how to approach PC templars (given all the blowback Paizo got over Agents of Edgewatch during the BLM protests, and templars are MUCH worse than that was!).
I could think of a number of ideas for the former, but I'm a non-American white guy so i wouldn't want my ideas to be the be-all-and-end-all without a good solid looking over by a qualified sensitivity reader though. And i can see the really obvious sticking point. Clearly one of the most blindingly obvious slavery-related plot lines in a D&D game is 'extract person X from slavery,' whether X is a PCs loved one, or has valuable information, or whatever. But one clear option for doing that would for the PCs simply to accumulate loot and then buy X off their current owner, and to do that, they'd need to know the cost. I reckon putting a pricetag on a person, in a D&D products, would be a big step too far for WotC. And there's the whole risk of trivialising the issue. Real slavery was a monstrously comprehensive and oppressive system. D&D slavery has an unavoidable vibe of 'if you haven't levelled up a couple of times and escaped already, you're probably a loser NPC'. I found the youtube series called 'African-Americans talk D&D' or something like that pretty enlightening on the issue. I didn't necessarily agree with all of it, but it made me think, and did make me more understanding of the point of view.