I believe it's a safe bet that any future Pixar worlds would try to go with original stories outside that of their original movies if possible, so let’s theorise!
-A Bug's Life: the movie’s ending allows a perfect spot for any potential follow-up stories to happen. The ants have to deal with whatever new threat the KHverse is throwing at them, with the newly crowned Queen Atta overseeing everything.
-Finding Nemo/Dory: could either happen during the gap between the two films or after FD. Dory’s memory problems could tie into KH lore.
-The Incredibles: would likely have to be post-Incredibles 2. New KH-specific threat arrises, the heroes get to work. Simple.
-Cars: ...I mean, if we absolutely have to (inevitable dumpster fire of awkward controls aside), it can happen just about anywhere, between 1 and 2, between 2 and 3, after 3, whatever.
-Ratatouille: may be difficult to work in the original movie as having happened, with Remy being in Twilight Town, and his history with Scrooge being a direct parallel of what happened to him at the end of said movie. But if they do, post-movie, simply.
-Wall.E: post-movie, could be set in the early days of the Earth rebuild period (the setting is still mostly dystopian-looking, but with noticeable signs of restoration). Wall.E and EVE being robots that seem to have hearts could be a theme.
-Up: post-movie, but we’d need an excuse to bring Carl back to Paradise Falls, which may be problematic since the house is still there, potentially undoing the closure Carl got at the end of the movie.
-Brave: post-movie. Badda-bing, badda-boom.
-Inside Out: post-movie, but the logistics of how we’d incorporate a world which is basically the inside of some girl’s head would be tricky to figure out, unless we put it in the Realm of Sleep or something.
-The Good Dinosaur: post-movie. Don’t really know, don’t really care.
-Coco: post-movie, and whoo boy what an interesting premise it could be. Here we have the Land of the Dead, a world where hearts seem to get a second chance at life before moving on!
-Onward: post-movie. Ian and Barley are up for more epic journeys, simple.
-A Bug's Life: the movie’s ending allows a perfect spot for any potential follow-up stories to happen. The ants have to deal with whatever new threat the KHverse is throwing at them, with the newly crowned Queen Atta overseeing everything.
-Finding Nemo/Dory: could either happen during the gap between the two films or after FD. Dory’s memory problems could tie into KH lore.
-The Incredibles: would likely have to be post-Incredibles 2. New KH-specific threat arrises, the heroes get to work. Simple.
-Cars: ...I mean, if we absolutely have to (inevitable dumpster fire of awkward controls aside), it can happen just about anywhere, between 1 and 2, between 2 and 3, after 3, whatever.
-Ratatouille: may be difficult to work in the original movie as having happened, with Remy being in Twilight Town, and his history with Scrooge being a direct parallel of what happened to him at the end of said movie. But if they do, post-movie, simply.
-Wall.E: post-movie, could be set in the early days of the Earth rebuild period (the setting is still mostly dystopian-looking, but with noticeable signs of restoration). Wall.E and EVE being robots that seem to have hearts could be a theme.
-Up: post-movie, but we’d need an excuse to bring Carl back to Paradise Falls, which may be problematic since the house is still there, potentially undoing the closure Carl got at the end of the movie.
-Brave: post-movie. Badda-bing, badda-boom.
-Inside Out: post-movie, but the logistics of how we’d incorporate a world which is basically the inside of some girl’s head would be tricky to figure out, unless we put it in the Realm of Sleep or something.
-The Good Dinosaur: post-movie. Don’t really know, don’t really care.
-Coco: post-movie, and whoo boy what an interesting premise it could be. Here we have the Land of the Dead, a world where hearts seem to get a second chance at life before moving on!
-Onward: post-movie. Ian and Barley are up for more epic journeys, simple.