Grand player of the Underworld is the best he can achieve. Doffys role more or less. He has ambition and decent strength but knows himself that he can't compete with admirals, yonko or even most/some YC. That's why he made Alabasta a place where he would have the terrain in his favor, i.e. desert, in the first place. And he was looking for Pluton to keep troublesome enemies out of his empire.
With that said I would like to see fully hakified Crocodile. With his DF mastery, intelligence and awakened/renewed haki he could be a great commander for the revolutionaries replacing Kuma but that's about his ceiling.