Mercurius
Legend
Yes, as much as a lot of older gamers look back on Kara-tur or Maztica or al-Qadim with fondness through rose-colored glasses that obscure the problematic parts, I think all those regions should be left alone and not updated for 5E, or a future 6E. Either do more MtG settings that are similar in flavor and theme or maybe even, however unlikely, a brand-new world. But they were obviously up to something before all this stuff blew up. They did not need a bunch of cultural consultants and sensitivity readers just for Theros alone or to adjust the PC monster races. Whether we will still get what they had planned, or it is just delayed, only WotC knows. Actually, back when the Tabaxi were updated to 5E, I was sure that meant something to do with Maztica would be coming out eventually. Maybe they can still do something with that, as of those three regions I mentioned, Maztica would be the least hazardous to update. Plus, unlike the other two, is there even a MtG setting with a similar theme?
I believe Ixalan is the Mesoamerica-inspired world.