^ Seems plausible, cept for one thing. Kakashi and "Madara" were face to face. Kakashi saw the Sharingan, and with his own he was have seen "Madara's' charka follow and instantly knew it was Obito.The fact that he hasn't said anything up until now means it couldn't be.
And if Obito was pissed off with Konoha, and Kakashi and Rin particularly, he would have lashed out instantly against Kakashi the second he saw him, instead of entertaining Naruto.\
Personally, I think Madara is a body jumper similar to Orochimaru, but instead of an actually body, he's using Zetsu's counterfeit clone bodies as a host.I'm sure Zetsu's not in Akatsuki because they need a guy to eat the corpse and do reece's all over the place. They are ninja, they are known for their stealth. He has a purpose for being there. And Madara also stopped him from fighting Kakashi, Naruto and Sakura. Why? "Because he's unfit to fight?" There has to be more to him then that the house plant of the group.
And I believe the First was just the most powerful Ninja at the time. What I actually think happened between their duel was that it ended in a draw. The fight left both of them broken, Madara retreated into the shadows, and Hiroshima went back to his people, and pasted the title of Hokage to the Nidaime, as he was unfit to fight nor protect any longer.