This is very likely to happen Sasuke doing Battle with The Past Hokages and Wining
1st off it a 9 out 10 chance it will happen because one Naruto and Sasuke will fight one final Time thus the Hashirama flashback is just to show us the hax fight btwn Hashi and Madara.
And when this Happen Sasuke will do battle against The 2nd which he can beat pretty easily...infinite Darkness only counter is EMS which Sasuke has, plus Sasuke is knowledgeable in fuinjustu so might just seal him up to byhimself
We all know he can beat Minato and Hiruzen...Susanoo and a few well time chidori...use tatics and skill
Because of proof that Sasuke will fight Naruto...its also proof that he will somehow beat or come close to beating hashirama before sealing him up again
What level will you put Sasuke on after these feats have been done...God-Teir,OP,Top 5 in the Manga????