You know what would be cool, and of course optional, is to have some sort of boss database. Suppose you beat the game, or get to the end of the game, that some database computer like Ansem's computer, could allow you to fight any bosses fought in the game. Perhaps, this could even be extended to the bosses from the entire series.
I Want This!
But to add on to this, there should be features that you can select.
Like say, fight more than one boss at the same time, Time Attack, Survival Mode etc. etc.
1,000 Heartless Fight
1,000 Nobody Fight
1,000 Unversed Fight
This would be great.