I'm not sure how much of Nomura/Sakaguchi's original scenario made it into the final game, but I was always given the impression it was changed substantially at some points (the original script didn't involve the death of Aerith and didn't include the character Tifa, for example). Of course, I've never read the original script so I can't really comment further.

I don't think anything like that exists for KH, at any rate.