Who is Tobi? As last written in Naruto 564 when Naruto asks who Tobi really is- he answers, "You can call me by my old name, Tobi, if you prefer. The war has already begun...My name no longer matters. Madara, Tobi....call me whatever you want. I'M NO ONE. I DON'T WANT TO BE ANYONE. ALL I CARE ABOUT IS COMPLETING THE MOON'S EYE PLAN."

Before this chapter was released, I believed that Izuana, Madara's brother, came up with this plan after Madara was beaten by the 1st Hokage. It seemed likely because the whole entire Uchiha power stems from two brothers of equal power in order to gain the EMS. Hence, Tobi's interest in Sasuke and Itachi. It seemed that those two were somehow working together to create this Moon's Eye Plan and retain Uchiha's title as the most powerful clan by restoring the power of the Sage of the Six Paths.

In order to make an educated guess as to Tobi's true identity you have to take in to account a few factors of manga writing:
1. Always expect the unexpected - the author needs to shock the audience and develop a new arc that can be explored and tie together the whole Naruto story. Lets get serious if Tobi really is Obito or Izuana we would all be writing mangas and would be extremely disappointed with the author and the manga,
2. Audience must sympathize with the antagonist - even with Orochimaru, Pain, and Danzou the author portrayed those characters as trying to change the world for better albeit by force
3. Myths are realities - The story of the Sage of the Six Paths is perceived as a myth, but Tobi's Moon's Eye Plan clearly alludes to the fact that this unattainable power is possible
4. The antagonist is always a super-villain that somehow connects every plot twist and has been around since the beginning.

With that my assertion is, Tobi is an acronym detailing that he is really the third son of the Sage of the Six Paths. As we all know the Sage of the Six Paths split his power, eyes and body, between his two sons and split the 10 tails individually so no one could ever attain his power and rule the ninja world. If Tobi is the third son of the Sage of the Six Paths, this could blind-side audiences and give the author the ability to create a whole new arc and plot line twist. Think about it, you have 2 brothers essentially heirs to the throne of power in the Naruto world, and then you have a third brother that is given no power and is forgotten. He is not accounted for in the myth of the Six Paths- "HE IS NO ONE. HE DOESN'T WANT TO BE ANYONE"-, which develops resentment and hatred within Tobi. Tobi feels neglected by his father because he has no real inherit power and can never gain the acceptance and love from him that his brothers received. So Tobi, feels the only way to be recognized by his father is to become as strong/stronger than his own father.

Not only would this surprise all audiences and allow the author to create a new arc to continue for several chapters, it would explain the truth behind the myth of the Sage of the Six Paths. It would also explain Tobi's motive. As we all know from Sasuke's story, a common theme in these manga's is a young man trying to gain his father's attention and be recognized as his son. And what better way to gain your father's attention than surpassing him.

It would also explain Tobi's interest in both Sasuke and Naruto, with both of them being descendants of the Uchiha and Senju clan's which are the two clans created by the 2 sons of the Sage of the Six Paths. He must need them to be his sacrifices in order to gain the true power of the Six Paths. This paves the way for the final battle of Sasuke and Naruto teaming up against Tobi and defeating him while the Uchiha and Senju clans finally gain peace amongst each other and peace in the ninja world.

Yes, this might seem like a wild prediction but it would shock all of the fans, create the necessary sympathy/understanding of the villain, explain the story of the Sage of the Six Paths and the creation of the ninja world, and tie together the beginning of the Naruto world to the end result of a utopian ninja world.