There may be a slight chance that Marco will join with the Red Hair pirates for the time being. He has lost both Ace and Whitebeard and might want revenge, but he alone isn’t strong enough.
During the Payback War the Whitebeard Pirates suffered an utter defeat against Blackbeard Pirates. Blackbeard is probably searching Marco to steal even his Devil Fruit powers.
Who would be the best person to be with while both hiding and waiting for the right time for a revenge? Shanks!
It may sound stupid, but I believe that, after they were on Ace’s and Whiteberad’s grave, they have joined and are now waiting for Luffy to arrive, so that they can change the system and the world together.
So what do you guys think?
*All rights go to the maker of this theory.