Any ideas who could have been the masked guy with long hair? He couldn't have been Madara since his hair was white and he was very old when Obito got crushed.
Very interesting question. A few days ago I put out a theory that the mask was used by both Madara and Obito to keep the identities a secret and to fool Pain into thinking that Obito was Madara and that "Madara" was therefore effectively immortal. Now, it seems like that might not be the case. Remember that Tsunade uses the transformation jutsu to make herself look younger than she really is. Madara could have been doing the same (again, to fool Pain into thinking that Madara is immortal). But, that seems a little bit less likely.
Two questions we have to answer now, if my theory doesn't work as well, are:
1) Why was the masked man's hair long for a while, if it wasn't Madara?
2) Why did Obito help massacre his own clan, when he didn't have a reason for vengeance like Madara had?
2a) If it was just a way to recruit Sasuke and Itachi to his team, why did he need them?