There are two ways I think he would be a main villain arc.
1. If there is a separate arc for Marine and WG to fall.
- I don't think this would happen. That would reduce a lot of WG forces. And at final arc I expect Revos, probably Law and Ofc Straw Hat pirates with Grand Fleet to be there. And for a final war that would be underwhelming compared to other arcs.
2. He takes WG.
- Not happening. He is loyal to his position and never cared about them. He also have no idea on many things like road poneglyphs, ancient weapons, Joyboy, void century.
1. If there is a separate arc for Marine and WG to fall.
- I don't think this would happen. That would reduce a lot of WG forces. And at final arc I expect Revos, probably Law and Ofc Straw Hat pirates with Grand Fleet to be there. And for a final war that would be underwhelming compared to other arcs.
2. He takes WG.
- Not happening. He is loyal to his position and never cared about them. He also have no idea on many things like road poneglyphs, ancient weapons, Joyboy, void century.
Think of it similar to Impel Down and Marineford, 2 separate arcs, same plotline. At the point where the head of marines are defeated, itd be time for the WG itself to fight, assuming Im, Gorosei, Kong, etc are powerful