I also think Jinbei is the most likely new crew mate. brennen.exe's reasoning is very good but that's not actually the thing that makes me think he's lined up for the next crew member position. For me it's about how will he fit into the Straw Hats and what will he bring that isn't already there. Hancock doesn't make any sense because she's totally one-dimensional around Luffy, would constantly be arguing (or being incredibly suspicious) around Nami and Robin, Sanji would be in Mellorine overdrive all the time, Brook will say "panties" every other word, Zoro will have nothing to say with her, nor will Franky. Chopper will just wobble around being cute whatever happens. So all she'll add is another target for Brook and Sanji (pointless) and she'll just be a female Sanji around Luffy. Any fight scene with Luffy will be screwed up by her running around worrying about him and blushing whenever he thanks her.
However, Jinbei seems to fit in more easily. There's no overwhelming reaction he'll have to any of the crewmates that would make things too predictable and flat, and no reaction he'll gain from them. He'll be like a father figure to them all, or maybe more of an uncle figure since they all already have father/mother figures as it is. He'll also add an interesting dimension to the current members. For example, I can imagine him and Zoro getting along due to their serious sides, he'll be a gentleman to the ladies and not just in a "I want to hump you" Sanji way. I can really picture him commenting on Franky's engineering ingenuity and Sanji's cooking with a sort of fatherly approval.
Then when I add all the stuff that brennen.exe has said, particularly that Fishman Island is an upcoming destination and that the slaver thing has been left open, and it all seems to natural to me.
@They:
other than Zoro occasionally being seen lifting weights and such, is there ever on screen training sessions? Why should Oda start now?
Well I do think it'd make sense in this one instance since Luffy mastering Haki seems to be an inevitable thing.
@Flagg1982:
lol
shishibukais will never join the crew.
Why are you people even entertaining that idea ?
You know it's never gonna happen.
And it shouldn't.
Well they've already shown that they're stronger than Crocodile and Moria. Hancock is "allied" with Luffy, so to speak, and her powers have no effect on him anyway. The Shichibukai aren't like the final bosses in a game or anything. They also don't have any kinship with each other so it's not like it'd be splitting up a proper group or anything. The World Government give the title out at will so someone can stop or start being a Shichibukai depending on their whims.