So, here's a thought. What if, and this is a big IF, "Tobi" is really....the Second Hokage? "Tobirama Senju" is his name, he was a master of space/time ninjutsu, he created the Edo Tensei...
For all we know, he could have still been alive during the 3rd's reign. Just in hiding. Maybe he had a complex against his older brother, who was always seen as the hero. He could have taken the REAL Madara's eyes and spent the years mastering them. Then he got Kabuto to help with the Edo Tensei because he never took it as far. He could have created a clone or some other way to "resurrect" him in case his soul was ever called upon by the technique. And the black hair could be a disguise. So he would spend years mastering the Sharingan of the most powerful Uchiha warrior of their time, created a technique that would be the firestarter of the whole war, and either !) Come out as himself and become the "hero", showing once and for all he is the best Senju, or B) Seriously want this "Moon's Eye Plan" to kick in, to finally bring a warped peace to the ninja world.