But realistically I'd see both films not coming back in the next games with the latter film being replaced by a world based on The Incredibles.
Trust me, if people complained about San Fransokyo being lifeless, then Metroville is going to be even worse. Incredibles (at least the first film) might have a better overall story than Big Hero 6, but its world is sooo boring. There is nothing about it that makes it unique. There are no set pieces, Villains are barely a concept, and the guest party members would just be Mr. Incredible and Frozone. If people were disappointed with only Baymax as a party member, imagine the reaction for the Incredibles.
Also, it wouldn't be hard to recreate characters that appeared on the Cartoon series to be in Kingdom Hearts. All new original characters still have to get approval from the original filmakers (who are currently working at WDAS). Plus many Disney Animators would know how a cartoon character would look like going from a 2D show to a cg feature length film.
There are way more adventures to tell in Corona and San Fransokyo, their setting alone is a testament to that. If anything i wouldnt be surprised if KH4 began only using films from 2010 onwards.
Disney Animation you have: Tangled, Ralph, Frozen 2, Big Hero 6, Zootopia, and Moana
Pixar you got: Toy Story 3/4, Monsters Inc (with sequel tv series in dev), Brave, Coco and Inside Out (???)
Lets be real, Disney saw KH3 as a way to advertise franchises and it worked. I have a feeling that the next game will still rely on the brand new Nostalgia these films will be getting. But hey, i only see it through a business lens.