Still, it's completely possible that these characters are disney characters. Just more important ones, like Donald, Goofy, Mickey, etc. Or, it could be disney characters who travels the worlds, like Merlin. And then, there is also the possibility of FF characters (Noctis and/or Lightning would be awesome :O).
If they are new original characters though, they better have a backstory, which is covered in BBSv2. Or, they better be presented in a way that's not too silly.... Maybe, Keyblade wielders from other worlds that sense the disturbance in the worlds go out to learn what's wrong and then find Sora and Co. or whatever. That wouldn't be too bad.