Hmmm...it would be interesting to fight Sora. But all the other secret bosses have fit in to the game's canon. How would Sora be considered a canon boss? (If it's a future Sora, like an adult Sora who traveled back in time, I'm gonna scream. The last thing this series needs is a time travel element for the plot. It has enough confusion as it is now).
Well, confusing as it would be, Sora did fight the LS... what BBS has the LS fight him back...? Course he'd have to lose, so it makes no sense...
Course, this would mean an extra boss fought immediately after the 'secret ending', so we may never know.
I dunno what to think... if we're still on the time travel thing, I'd have to say Young Xehanort on Destiny Islands. I think it would be refreshing to have a secret boss on DI...
Maybe... Xehanort's nobody? Yah, I know, its Xemnas, but Xemnas was the body created when Terranort became a Heartless. Xehanort gave up *his* body to possess Terra, where did it go? After all the things that would promote Xehanort to
Magnificent Bastard-om, I wouldn't brush him off for not having 'a strong will'!