Yeah, the Tobi = Obito theory has been around for awhile. My guess was that he might be Madara's actual brother. He may have sacrificed his eyes for Madara but they only implied he was killed by a character we already know has been lying, and who else would be this fanatical to help Madara cause? Since the real Madara seems to know who this imposter is and even been stated they are working towards Madara's actual goal in life, I think its a plausible theory. I'm more curious to know where Sasuke fits in all of this, he's been out of the manga for a very long time and they keep implying he's important to Tobi's goal but nothing so far.