have something in comen, maybe
madara resurected by pain...BINGO!
... but now that I think about it, IF Danzou were Madara, he wouldn't even HAVE to conceal his right cause because wouldn't Danzou be able to turn his Sharingan off?
well truthfully, without pulling up the tobito stuff, how can you explain why he is so young looking for a guy that should be about 90? Madara and Danzo could very well be related and they could even be brothers, nothing like 2 faked deaths to throw everyone off.
I think that he/they have the rinnegan as well, but I'm, also a bit crazy so...