I think the best way to put Weevil in the story is for him to attack Sphinx looking for his supposed "inheritance" from Whitebeard's fortune. We already have Marco "the protector of the Island" in Wano so Sphinx is pretty much vulnerable from an attack. We might even stumble upon a Road Poneglyph there since its last appearance is in Fishman Island and it was formerly Whitebeard's territory.