I just feel izuna has a part in this.
No, this is not a Obito is really just Izuna in Obito's body and he is actually the real Tobi theory.
I was an original Obito=Tobi theorist, like all the way from the beginning of Tobi. And considering the fact that when Madara greeted Obito he called him "Obito", not "Izuna" I think it's safe to say Tobi is really Obito.
But, I just feel that Izuna has a bigger part to play in this whole story. No, I do not think that Izuna is alive, but he has to have a big part in this. Maybe Obito is his great-grandson, or maybe he didn't actually sacrifice himself, I seriously don't know.
But the fact that we, at one time, compared Naruto to the 1st Hokage and Madara and Izuna to Sasuke and Itachi its hard to just skip over a character as much as we have Izuna. We haven't exactly develped the 1st Hokage greatly or nearly as much as Madara but at least he has been seen more than Izuna.
Theories? Thoughts? This is just my opinion, I'd love to hear yours. If you don't agree why not?