At this year's Japan Expo, Tetsuya Nomura was questioned in an interview conducted by Gear Nuke. Nomura discusses a number of things in its duration, but nothing was more interesting than the topic of what worlds might be included in Kingdom Hearts 3. Though Nomura and his team have been quiet on the subject so far, and this interview doesn't serve to change that, it does bring some interesting facts to light that may not have been looked at so closely.
Disney, who is a major component of the Kingdom Hearts machine, recently acquired both Marvel and Lucas Arts. While the money spent to purchase both of these companies is obviously of note, the possible implications for Kingdom Hearts as a series have grown tremendously. This was the focal point of the interview for a time, though Nomura generally responded in a way that didn't allow much light past the veritable canopy:
Nomura said, "Of course it would be great if we could add those licenses as well. But there are lots of rules and restrictions by Disney so we can’t actually put everything people want, so it’s a quite difficult decision but we’re gonna prepare some surprises for you so, just wait for the informations."
We wouldn't be surprised if Disney tried to keep Kingdom Hearts 3 limited to more classic Disney tales, but there are only so many worlds for gamers to explore. Throughout the course of the first and second games in the franchise, Square Enix and Disney have used a lot of those resources. With all of this taken into account, it seems almost inevitable that Star Wars or Spider-Man make an entrance into the Kingdom Hearts world at some point.