[ZGoten]

^Well, most people who believe in the Obito theory don't think that Tobi is actually Obito, but rather that it's Madara in the possession of Obito's body, because his old is, well, not good enough anymore. We've seen body transfer jutsus already, so it wouldn't be a surprise if Madara would actually possess another person's body.

However, with the latest chapter's flashback, the Madara-Obito theory got a mature kickback, due to the fact, that Tobi already possessed a full-grown body, just a year at max after Obito's death (if I didn't mess up on the timeline). There are still possibilities though, like Madara switching bodies from time to time, it's just become more unlikely, that Kakashi's old buddy's serving Madara in his death.