Who's in the 6th coffin???
I don't know if this has been discussed somewhere else or not (forgive me, i'm new here )
Oh well, I know it may be wrong, but I personally think that in that coffin is Izuna Uchiha aka Madara's younger brother.
Why else would Madara react like that once he saw it?
Personally, I find it more beleivable that other theories such as that it's Madara'a body or Obito's or Shisui's (although it may be this last one either, his body was never found remember?)
Anyway, what do you think?