I feel like even though they share the same eye the person under the mask is NOT Obito... I feel like the man under the mask is one of the ninja from Iwagakure that Kakshi fought. Either the one who turned invisible or the one with the blades in his sleeves. It seems like Kakshi fought him but did not kill him (it looked like it, but was never confirmed) and he fell into the cave where Obito's body was. Whats to stop him from taking the other eye? He caused the cave in so he uses Earth style so he could move the boulder, he is older than Kakashi and talked to him AT the battle. Yes, his hair is a different color but that can be changed... The boulder crushed Obitos Right side BUT I do not think it crushed his eye... That would mean it crushed his skull which would of killed him instantly. I think his eye survived... I think between him, the ability to get Madaras and 1st hokage's DNA and Orochimaru a lot of things are possible... I feel like the scroll they found is a secret to "HOW" Tobi came to be with his powers. Now that I think about it it is probably the one who turned invisible... Remember the Sharingan can see through his Jitsu and that is how Obito "killed" him so naturally he would have a hatred of the Uchiha since they are his main rivals to his jitsu... So many options...