Hopefully KH2 is beginning to follow the path of the Final Fantasies--in almost every one, you control more than one character at some point. Example: Controlling Zell, Quistis, and Selphie in addition to Squall during the end of Disc 1 and beginning of Disc 2 of FFVIII.
We didn't control anybody but Sora in KH1 (yes, his Heartless form counts as Sora), but now that we've seen BHK is a playable character, perhaps we'll get to control more characters. For instance, it's been said that Cloud's side-story will be very "entertaining"--maybe we'll get to control Cloud or Leon at some point?
If not that, then hopefully we'll be able to fight alongside them or fuse with them. It always drove me crazy that Leon sort of abandoned Sora after busting out of the hotel before the Guard Armor fight--he would have been really useful as a party member until the Third District.