I'd be very disappointed and like mike said then we'd have to go through two chapters of explanation then more flashbacks and shit. Plus it would just be anti-climatic because, I'l be honest with you, I couldn't give two shits about Obito.
Or what if this whole time it was really one of Naruto's shadow clones and Naruto was behind everything? Or what if the whole thing turned out to be a dream and Naruto is just some crazy homeless dude? Or what if this whole time Tobi was Gamabunta?
Not mad at all... It's actually the most logical and hinted ID of Tobi (At least partly. We know as fact that, at least his left hand is a white Zetsu's...) ... U_U
I would be somewhat anoyed if it was Izuna, 'cause that would be predictable as hell... oO