Ok, I finally have my theory on Tobi's identity.
Tobi IS Madara.
We've been trying to figure him out forced to the fact that since Edo Madara was revived he must've been someone else. We thought of anybody possible, trying to cope with all the possible explanations, guessing and guessing about any possible Uchiha or non-Uchiha.
Kishi's been trolling with us all the time.
Tobi IS Madara.
He never lied to anybody. All he said was true.
Madara awakened the Rinnegan short before dying. He read all the secrets on the Stone Momument. Who knows what secrets, aside the one of the So6P story, that monument reveals? With the EMS you discover the Rinnegan everyone thought being only a myth really exists and how to evolve into it (it's the logical step forward of a quest). What could have he read with the Rinnegan on the stone, who knows? How to prolong your life by transferring (if only a bit) of yourself (part of soul, body, who knows) into "something else"? With something else I mean Black Zetsu. Why don't we ever see black duplicates? Zetsu is not someone, is a something. Completely made out of the First DNA, perfectioned during the time into Zetsu, a useful servant.
Tobi is of course made (we don't know how much) of Zetsu's DNA.
Madara was pure genius, he must have planned how to survive "becoming" Tobi. Doing researchs, experiments, sharply plotting his come back.
Madara is somehow living inside this Tobi-body which is made up by Zetsu (First cells - to keep the Rinnegan activated and fuel it with the most power possible), has a Sharingan (probably not an EMS but we've never seen) specific for S/T jutsu, may have a third eye, sure he has now a Rinnegan instead of the Sharingan lost for Izanagi).
Madara was the best Uchiha ever. He could know all of the Uchiha ocular jutsus. He was able to awaken the Rinnegan. Legend.
Madara died and left what he could into this body he carefully prepared. He gave Nagato the Rinnegan since he wanted to test it and most of all he wanted to keep it safe and close (Nagato was from the Uzumaki clan, strong life, descendants of the First, he had to be the front leader behind Akatsuki). In Tobi's shape he couldn't use it properly. He only can use one jutsu per Sharingan (yes, per Sharingan...), he has lots of Sharingans collected in order to stock them and preventing anyone else from getting them, using if he needs them).
Madara was desperate to prolong his life since he managed to awaken the Rinnegan. He wanted to finally be superior to the First. He read on the stone with the Rinnegan he could become the Ten Tail's host.
He surely wants to complete his eye moon plan.
But Kabuto revived Edo-Madara specifically for a reason: threaten Tobi and gain hedge on him. Kabuto failed. Madara revived through the Edo and he's now free.
He's been dead since, how could he know how things turned out? He senses the Nine Tails and wants to to control it. His consciounsess and memory are not updated.
Madara died short before he started controlling the 4th Mizukage. He was still gathering the Tailed Beasts in order to become the Ten Tails Jinjuurichi. He died and left the rest of the plan to what he called Tobi. The name Tobi IS from Tobirama, because Madara planned for Tobi to use the Sharingan with S/T jutsu capabilities, that's what he only needed from "then" on. It's a mock of Tobirama's name, who was the master in that tecnique Madara surpassed. Minato clearly said it, he was able to defeat him only because Tobi proved itself not being strong enough for him within Tobi's body.
Since Madara has been revived, Tobi has no more meaning in calling himself Madara if the REAL one is around. So "he is NO ONE" from that moment on.
Tobi is worried about what Madara could do when he meets him, there will be TWO people wanting the same thing.
The Outer Path was meant to be used on Madara by Nagato when he was strong enough to revive him if the time has come for the Tailed Beasts to be gathered by Akatsuki. Then he could be alive again and finally become the Ten Tails' host and cast the infinite genjutsu.
But something went wrong: Nine-Tails and Eight-Tails not captured, Tobi had to start a war because he didn't manage to accomplish the mission. Nagato betrayed them and used it on Konoha's people. Ability gone.
Madara's going to be furious when he knows all these things. but hey, he's alive again and immortal! Perfect situation for completing his plan.
Tobi is worried because he's going to confront himself (the real Madara) at his best.
Kabuto's role is crucial since he revived Madara powered up.
There's one interesting thing I noticed about Kabuto. When he summons Edo-Tensei Madara, their first dialogue is to be reinterpreted: Madara was supposed to be brought back by Nagato via the Rinnegan. He discovers he's under Edo-Tensei and supposes only one person could have done it because the plan was not going well: Orochimaru. Kabuto says he's his "servant". He's referring to Orochimaru because he was the one working with Madara. They were looking through the same things (immortality, sharingans power). Orochimaru wanted Itachi's Sharingans (they were the best he could be capable of stealing) and has always been twisted and unpredictable.
Orochimaru will play a decisive role in this war. He may be lying when he says he's got no interest in this war but there's a chance he doesn't want to get involved with immortal Madara. He's definitely going to do something unpredictable, Orochimaru.
And yes, immortal Madara has a Curse Mark.
And yes, Sasuke wants to meet them: Tobi and Madara, after his little trip with Orochimaru.
Now, the final: if Tobi IS Madara, how come Tobi didn't know how Edo Tensei worked while Madara managed to release the contract? Was he fooling Kabuto? Why?
Orochimaru is somehow involved in it. If Tobi was created by Orochimaru AND Madara, Orochimaru must have been tricked Madara somehow.
Now, the conclusions: I tried to put all things together from the perspective that we've been looking too far from the real evidence. We've been under continuous deceptions from Kishi and it all started when we assumed Tobi was lying about being Madara.
I'm very confident that Orochimaru is deeply involved in it. I can't still be so sure about the kind of involvement, but in its simplicity I think the're still so many secrets to be revealed that goes in the direction I tried to trace with this post.
I know there are many uncertainties in my theory and some points should be more convincing but, in the end, I think Tobi IS Madara himself.
+rep to whoever will read this to the end.
