Don't forget that Madara was a member of Akatsuki with some very interesting characters:As I said, I wouldnt write off your theory though like I indicated above, that the probability of that is highly unlikely.
In order for your theory to work Madara would require :
A. A body transfer jitsu (In order to consume/take over another's body).
B. A resurrection jitsu(In case Obito is deceased).
C. If B is not applicable then A regeneration jitsu would be required anyway, far beyond that of Tsunade to beable to regenerate squished body parts.
D. As well as a re animation jitsu in order for him to bring back his old appearance .
Pain: Who was able to animate and control 6 corpses at once to fight for him
Orochimaru: Who had a body transfer jutsu (and millions of other Jutsu)
Hidan: A bonifide immortal
Kakuzu: Effectively immortal, extends his lifespan by stealing body parts (especially the heart) from dead opponents
Sasori: Transplanted his heart into a puppet and got rid of his body completely. It's not mentioned whether this operation was expected to give longevity or immortality, however.
And let's not forget that if Tobi really is Madara as he claims, he is well over 100 years old and apparently in great condition.
I'm just saying, considering the techniques we have seen in other Akatsuki members, it is not entirely unlikely that Madara is somehow using the crushed and discarded body of Obito. Maybe he transfered to the body (like Orochimaru), maybe he just stole a bunch of parts from it (like Kakuzu and, unrelatedly, Danzou), or maybe he is using it as a puppet (like Pain). None of these are impossible.