First off, since there hasn't been a Pixar world, character, power, ect. in the entire 10 year history of the series, I'm going to assume that for whatever reason, Square Enix either can't or won't use Pixar material (although I personally think both "The Incredibles" & "Brave" would be good fits).
Gargoyles - As it was a TV cartoon instead of a film, it probably has no chance of ever appearing, but it would be a great fit for the series. A well told tale involving both anchient magic, and advanced technology, it's a really good show. Also, there's at least 3-4 big villains, so the world could have some longevity in the series (since they wouldn't have to spam the same bad guy). It's really well animated, & I suggest you check it out, to see how well it would fit (first 2 seasons only. The show's creator left Disney after that, so the story & animation both suffered greatly in the 3rd & final season).
Wreck It Ralph - I haven't seen it yet, but it's set inside video games. Sure, they'd have to get rid of the licensed cameos (most likely), but it practically has 4-5 worlds within itself. Could possibly be good as an eventual replacement for the Tron worlds.
Also, I would eventually like to see the Destiny Islands world opened up a bit (so you can actually go to the area where Sora & co. live), and I eventually expect that Wonderland will be updated to fit the theme & look of the live action Alice in Wonderland from a few years ago.
