I'm about halfway through a 5e campaign using Theros and have thought about a Dark Sun one myself. I'm of two minds about going the 5e route or the 2e route.
The argument for 5e is that the players are used to it and like the more modern D&D-isms such as everything using the same type of die roll and having tons of mechanical character build options. Also, as I look at Dark Sun, I can see that out of all the old settings, Dark Sun lends itself best to the "moar powerz!" approach of modern D&D. So, I started putting together some notes on what it might look like for 5e. I know other people did conversions, but I'd want to do my own interpretation because even TSR Dark Sun was only good for the first boxed set or so. I'm still working through classes and stalled out a bit.
The reason I stalled is my usual problem - I've grown to dislike modern D&D (anything from 3e on). I'm just not a fan of the new way they do spells, or hit points / healing, or all the powers / character options. Modern D&D versions stuff characters so full of powers and healing that the only kind of game they support well is a dungeon with X encounters per day which isn't always how I want to run a campaign. It's not that I can't run a less combat-focused game, it just doesn't work as well when all the players want to use all those cool combat abilities. In that sense, I prefer 4e over 5e because at least it leaned in to the whole "nothing but dungeon battles" focus. And then there's the digital tools, which I also find very limiting as a DM. The players end up relying on them to manage their characters because of all the extra character build complexity, but then I either have to do everything by the book (and almost by every book WotC produces) or I'm spending a ton of extra time and effort working against the grain to try and explain what content I'm using / not using and how to handle it when a rule or item or whatever isn't supported by the app. The app thing soured me on 4e once rules randomly changed between sessions (which they appear to want to do again for One D&D). Anyway, what it means is that my 5e version will need to be scaled back a bit and use some AD&D-isms so that I can run the game I want, and they won't need (or be able to use) the app.
So, then I moved back to looking at AD&D 2e again and seeing how I might adjust that to present the material in a way the players might go for with my own custom-written player's handbook. They'll definitely want ascending AC with attack bonuses over descending AC and THAC0. And I'll probably need to give a few more character options. But AD&D has its flaws, too. The first is that proficiencies are a fairly poor skill system (most RPGs do that better). The second is that AD&D psionics rules are dreadful. I'm still debating how I want to handle the skills/proficiencies thing but for psionics I'm just going to use the Palladium rules instead (circa original Rifts).
Once I complete the AD&D version, I think I'll go back and see if I can finish out the 5e version. Then I can compare to see if I'd prefer a more D&D 5e approach with some AD&D-isms or a more AD&D approach with some D&D 5e-isms.