Dark Sun: Now the good stuff. Yes, this settings got its blemishes, most notably slavery. However, this is something D&D hasn't shied away from (Out of the Abyss has too much of it frankly), and I believe if the setting is developed with cultural consultation, it can be updated pretty easily. Well it be rebooted entirely? It's happened before, and I think it's fairly likely so it meets some 5E rules standards. It's got loads of potential PC options, psionics are a potential new class, loads of new monsters, easy to write a new unique adventure for... compared to Mystara, I think this is medium risk, high reward. Easy contender for slipcase format. I don't think it makes much sense for mass combat (armies exist but they don't clash frequently), but ironically D&D Onslaught (kind of gladatorial in some ways) weirdly fits. And it's one of the two remaining most popular settings, I think it's happening it's just a question of when not if.