It's hard to say... if I were to take any Obito+Madara theory it would be the "Madara in Obito's body" or nothing at all.
Tobi and Obito are almost anagrams. That's probably the weakest clue of all but I feel as though it's still a clue.
It would tie in Kakashi Gaiden, which would be convenient, but I wouldn't be surprised if the Gaiden (side story) remained simply that.
They have kinda similar hair. Tobi's alternate personality is very light-hearted. Again, not very strong clues.
Tobi's right eye is the one he uses, Obito's right eye was the one that was crushed... but if he was being used as a body, he wouldn't have his other eye anyway, as Kakashi has it. So we can almost conclude that both eyes were effectively lost (or at least one might easily assume that.) If Madara somehow replaced the eyes with his own, then why would he have only replaced a single eye? The most sensible thing (other than discarding the theory) would be that Obito's eye was somehow not destroyed. I suppose it's reasonable since if half of his head was actually "destroyed", he would've been flat out dead.
http://img233.imageshack.us/img233/5322/obitozr6.png
Somehow...? Then again, crazier things happen in Naruto.
Against the case... well... Obito wasn't exactly the freshest Uchiha corpse, nor the most elite. He was also a child, and he died in a fairly random place in the wilderness, with most of the bones in his body probably broken. It seems rather unlikely that Madara, floating around all Voldemort-style or whatever the hell he was doing, would have ever chosen his body. The problem lies here, in how little we know of Madara: did he lose his body after fighting the First Hokage? By what method does he remain immortal? Just what was he doing with Itachi? One can't place too many limits on a character with powers like Madara. If he's capable of moving his body through dimensions or teleporting or what have you, who knows what his limits are?
Also, in the manga, Itachi says to Sasuke: "Though he lost the battle for control, he remains alive and well, as do his eyes, and their power."
The idea of changing bodies just doesn't seem consistent with the whole power of the eyes thing....
I'm sure there's a lot we'll find out in the next issue that might give us some clues at least.