At EOS final battle, the strawhat aren't the only main force, RA and bunch of other prominent figures will play a role
Luffy obviously fight the big bad boss, either Imu or BB
Rest of the opponent for other SH is unknown for the time being.
If Mihawk is truly the last opponent for Zoro, then he fights.
If not, the last opponent for "WSS Zoro" would be a guy with a sword with broken/hax power, similar to King.......that Zoro needs to overcome even after he claim the title of WSS.
Sanji opponent will be whoever weaker than the opponent of Dragon, Sabo, Law(if he's still there), other important characters etc