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this viz page suggests that madara's trump card has something to do with hashirama, maybe madara absorbing him so as to gain a sage mode welding body and become perfect or something like that
note that hashirama and madara are now alone in the barrier (i am assuming that they didnt get out as they didnt have naruto's chakra) probably regenerating, madara could seize this opportunity as hashirama is vulnerable
another thing that i noticed is that last two chapters there has been Naruto-Hashirama comparision
could this be a hint that Hashirama now has no significant role as Naruto has somewhat reached his level/become like him
this could make it easier for the alliance side to 'lose' hashirama to madara