Wow, okay, that changes things quite a bit.
So, going into this episode, what I thought was going on was this:
1. The Masked Man was Madara's spirit inside of a White Zetsu body.
2. Kabuto's secret weapon was either A. The Sage of the Six Paths, or B. Madara Uchiha's body
3. If it was B and Kabuto activated the Reanimation, Madara's spirit would be pulled out of his Zetsu body and into the Reanimation, which is why he acted afraid when Kabuto showed it to him.
But clearly, B. was the case, but when activated, nothing happened to the Masked Man, so obviously, the Masked Man just plain isn't Madara.
So who is he? Some other Uchiha still presumably. Would have to be someone we thought was dead. Could be Shisui. Or Madara's brother(who they never actually explained how he died. Or IF he died. We just know Madara took his eyes). Or could be Obito.
Madara owning the crap out of everyone in the next episode preview is to be expected, but looks like he's managed to get the Rinnegan somehow by the looks of things.
Another eye swap?
Uchiha Orbito all the way. It's cool that Naruto is back onto canon material, but it didn't change the fact that seeing Naruto arrive everywhere to own white clones for 30mins was lackluster.
If it's not Isuzu-chan Mii~
Missing is the best form of attack right?
I was thinking that the masked guy could still be a Zetsu clone of Madara that he implanted his will, eyes, and a massive amount of chakra into and that his goal was to retake control of his body at some point. His look of shock was at his wonder as to how some shitty wanna be Orochimaru found his body, but also excitement at the possibility of "regaining himself" so to say. Could be horribly wrong though
Actually, yeah, that's quite possible.
If there's one thing the 4th Hokage showed us, it's that a spirit the Naruto world doesn't have to be in one piece in order to still function and maintain it's consciousness. Because even though he's sealed away inside the Death God, the piece he left in Naruto was still fully capable of functioning.
In fact, it seems like any vessel that holds a part of your chakra also holds a piece of your consciousness. Your chakra is like your "ghost" as it were.
So yes, the Masked Man could just be a Zetsu that Madara put a piece of himself in before he died.
Given that we KNOW his body is Zetsu like, I think that's actually the best explanation right now.