I know I have a Zetsu theory out (like everyone else :-p ), but looking at some of the facts of the story, and understanding a bit more about the Uchiha, I find it interesting that there is a question as to whether or not Tobi is infact an Uchiha.

Actually, looking at the details, I find myself wondering just who would have the 2 characteristics that I find Tobi does have in terms of both strength and motive. We know Tobi has substantial strength based on the fact that having both the sharingan and rinnegan constantly active hasn't completely depleted him (this was prior to the massive w.zetsu invasion). We can also toss out there that he may have a vendetta against the Uchiha considering his participation in the massacre, as well as his willingness to drag the Uchiha name through the mud with all the crimes and things that he's done, as well as take advantage of Sasuke.

So to address a few things, I would argue that his POWER, the power to be able to get to the tablet and read it, while not being an Uchiha may come from being a rogue Senju! We see through the series that the Senju are always portrayed as the "good guys" and the Uchiha (with Madara leading) are portrayed as the "bad guys," but we never see the potential bad guy Senju! Having that power, the Senju would be able to sustain the ocular jutsu, get through to where only the "elite" Uchiha would to read the tablet. We could also argue that he would possess the proper linage then to potentially possess the 2nd's S&T jutsu ability.

The next thing would be motive. For a lack there of a better words, trying to pin down a motive for this is actually harder than it seams. Tobi would control the world, but to what end? he isn't after riches, land, but simply wants to direct the world in an image he sees fit, but why? From prospective of a twisted "younger son" or Senju prospective, one could argue that he believes it was always the SoSP's vision to have his successor create peace. Now, one would argue "but the elder son wanted to do it through power" however one could define that as "ruling over them" as in conscious subjugation through a more feudal structure or "single nation." For this particular (apocalyptic) rationale, one could argue that this happening would give the illusion of peace and go with the idea that through love the ends justify the means.

It may be out there in terms of all aspects of the theory, but I still think perhaps it may be valid considering the fact that we don't really see a whole lot in the representation of the Senju in the village outside of the 1st, 2nd and Tsunade. Perhaps that means there was more dissent in terms of agreeing to peace with the Uchiha than we are lead to believe? who knows!