I wouldn't mind Big Mom escaping Wano and being the villain at Elbalf. Luffy could best her 1 on 1 there. She has connections to the giants there and it would make sense that Big Mom, the first Yonko that Luffy encountered in the New World, is the first one he faces on equal standing. It would bring the conflict with Big Mom to an end and give screen-time to the members that didn't get any in Whole Cake Island and Wano. Though, with One Piece ending in 4/5 years, Oda might not have time for a +50 chapter arc with a Yonko as the villain. Maybe instead they'll just meet Shanks there (if even).