I agree but I also disagree. I think the BB pirates will be the final villains, but... zoro final opponent need not be the shiryu. For instance, if shiryu and zoro have a fight before reaching raftel but then BB and luffy have a fight on raftel to see who will reach one piece first. If the war then happens after that and the war doesnt involve luffy and BB but everyone else then in a sense the war is pirates aliied with various factions fighting to keep the marines from reaching raftel and preventing a PK from happening. then zoro could be part of that fight and he would clash with mihawk then.