My guess is that 'Tobi' is Izuna Uchiha. The only proof we have of his death is the word of 'Madara'. To fake one's death its obviously necessary to propagate such a rumor. My theory is that Zetsu witnessed the battle at the VoTE and retrieved the eyes, while enjoying a snack, for Izuna. Unforeseen problems arose with the EMS 're-transplant' leaving Izuna at diminished capacity. He poses as Madara for obvioius shock-effect advantage. I agree that Kabuto knows what we all want to know. And that is the truth behind the mask of Tobi. He keeps dropping hints.
Izuna was left with diminished sharingan and was on a quest of vengence and an upgrade. He used Zetsu to be on the lookout for any and all Sharingan of fallen Ninja. He found Obito's eye intact, attached to his crushed body and took it from his dead corpse. Again a snack. Zetsu is impermanent to solids--easy for him. Obito died and is not Evil.
'Izuna-Tobi' made a deal with Danzo. I believe Orochimaru, obsessed with forbidden techniques, was involved with and an agent of Danzo, employed as his 'Dr. Frankenstein'. The deal made to 'harvest' the Uchiha sharingan as weapons... The ultimate Forbidden Uchiha tech--Izanagi. A Tech that closes the eye permanently. Requiring a large supply of disposable Sharingan. The 2 split the booty, entered into a mutual non-aggression pact and rendered a potential threat into non-existence. I believe Orochimaru joined Akatsuki with the orders from Danzo to retrieve Itachi's sharingan. Later, Oro went rogue and desired the Sharingan for himself, pursuing Sasuke.
Izuna, being the equal of Madara and one of the 2 firsts to awaken MS, knows the Secrets of the Sharingan and the history as well as Madara. He took it upon himself to surpass his brother once and for all. To go one step further than Izanagi. To become the 'equal' of the So6P. Insane, but logical.
