I agree wholeheartedly with the Tobito theory, more because of the tiny details that match up, rather than the big picture (though a Kakashi-Tobi fight would be pretty awesome at this point).
The use of orange (goggles -> mask), the eye hole over the eye that Kakashi didn't take, personality...all those kinds of things.
And even if his body was completely crushed beyond repair, Sasori or Kakuzu could have done something to fix him up. Slicing Tobi in half did nothing to him--maybe because he's really fast and faked getting sliced, or maybe because there's nothing there that can be damaged. A puppet's body could be detached with chakra and reattached after the sword had passed through it.
You have to consider what those bolt-ish things in Tobi's original outfit were for. Maybe holding his joints together?
I don't think the Sharingan would have to be an issue, though--an eye is much more delicate than an arm, and more difficult to save. He could have had a new eye transplanted, like Obito's Sharingan that Kakashi has.
=___=; no matter what you say I do not agree with this theory Tobi=Tobi | Obito=Obito
TOBI=TOBI | OBITO=OBITO
Well, time will tell so long as HE DOESN'T FRICKEN DIE IN THE NEXT CHAPTER!!!