I see why everyone likes and wants Hancock to join, but I really don't see it happening. Every crew member has had distinct purposes in joining and generally when you look back and watch or read it again you see all the queues which point to them being future nakama. Why do we need Boa Hancock? She'd be as useless as Ussop and as distractable as Sanji. (note: i dont really think ussop is useless, just less useful…).
The character that seems to me as being presented as a pre-crewmemebr is Jimbei. The Straw Hats need someone who can take on enemies in water esspecially seeing as they are going to bring their ship to fishman island. Jimbei was instructed by Ace to protect Luffy! Jimbei has no crew, or other responsibilities which will ultimately keep him from joining. He knows more about the new world (and world in general) than any other character even close to being a possible nakama.Also I think the fact that the Straw hats wanted Vivi to join and her not joining says nothing about whether Hancock will or not. The fact of the matter is that Vivi decided not to join to save her country, and in fact, if she were the kind of person who could condemn an entire country to suffering just to go on an adventure.... then she souldnt exactly be straw hat material now would she? I dont think Boa is Straw Hat material, I think shes selfish and would only join the crew to be near Luffy
we need her as a capeble fighter. how could the crew not benefit from her kings haki. zoro's reason of joining is because hes very strong. Well Boa is strong also.