Welp, Spelljammer, so that's great!
I'm not a huge Dark Sun fan, but I would eagerly buy that setting as well. Assuming that they ever settle on how they're doing psionics, of course.
I'm pretty sure psionics are decided. They've gone ahead with the subclasses and feats route in Tasha's.
Dark Sun would be an easy sell I think, and most of the work is already done. If we assume the slipcase format Spelljammer used, we'd get an adventure book, a bestiary, and a setting guide. I could see the last book having the Mul race, gladiator fighter archetype, elemental cleric domains, a bunch of psionic feats with maybe another psionic subclass or two, and the templar warlock pact. Defiling magic would likely be in there as well. The rest would be setting details, likely focusing on the Tyr region.
The adventure could feature expanded rules for survival and exploration.
The bestiary would feature a handful of our favorite Athasian monsters. Gaj, Tembos, Braxats, Gith, Elemental drakes, beast-head giants, so-uts, nightmare beasts, and so on.
