We all should of known it was Obito. Here are some facts. 1. The letters in Tobi=Obito-o 2. Kakashi's kamui jutsu is the same as Tobi's jutsus. 3. The reason for showing the story of Kakashi's childhood as a Jonin. These were the big hints.
yes 2 of the 3 were big hints but 1. "Obito Obit Tobi" was just a lazy guess that turned out right but to me Tobi is not Obito he is just that to me Tobi nothing more nothing less i love Tobi but hate Obito so to me Tobi is just Tobi Obito is just Obito nothing will change that (sorry if it seems i am getting mad at you i am not just with trolls reading comments you want to think ahead of time is all so Tobi = Tobi and Obito = Obito to me nothing more nothing less is what i am saying but i do know about the new book it was sad for me i wanted Tobi to be a new guy named just that Tobi Uchiha so that is who he will be to me nothing wrong with that is there)