They've already shown Disney Princesses, storm troopers, and MCU characters in more than cameo roles in the second movie, and the first one had Zangief, Sonic, Pacman and more. Canonically, seeing Sora and company show up in the next movie wouldn't be at all out of place. Hell it wouldn't even be out of place to see the Final Fantasy characters from the KH series show up given how many IPs have crossed over at this point.