I want the last crew-mate to be a girl. But not for the boobs, Nami and Robin fill that plenty enough. I'll even take an ugly girl but I'd prefer a pretty girl BUT NOT FOR THE REASONS YOU THINK.
When girls especially pretty girls are put in dangerous situations people will naturally, at some level be it consciously or subconsciously, feel more tension because we think they're more delicate and innocent. And it's quite pervasive in shonen as a whole. I personally don't like that very much even if some may think it can't be helped since that's the genre. I WANT to see more girls being brutally beat up as much and just like the guys AND them doing some brutal beating up of their own. Why did I start with getting beat up first? Simply put, I want women to be on the same level as guys, to be able to assume the same risks as men. Now I'm not saying I liked it when Spandam was mercilessly kicking the shit out of Robin, that was repulsive as it was intended to be. And of course I appreciate that in the real world and manga which are real worldish, females ARE biologically weaker and more delicate than men, at least young women. But in a fantasy series like One Piece where musculature clearly doesn't matter when you have people able to chuck houses or push apart buildings (which as you know, no amount of human muscle will allow and especially without extreme damage)? And more importantly, I want to see more women get in a fist fight and get a good punch to the face and imagine the gasp of the audience which stops midway as they see the girl smile, shrug it off, wipe off the blood off her face and punch back like it was nothing and the awkwardness of the audience as they don't know how to feel. It's a main reason why I like Negima or Change 123 or Blade of the Immortal (yes I know this one's seinen) or Kuroshitsuji. They kick so much ass, you forget they're even female. They're not treated any different most if not all the time.
Bottom line I just want to see more women kicking ass and getting their ass kicked especially pretty ones. I just find the notion more fun and interesting that a pretty woman can duke it out with the best of em. Where after some time, the gender doesn't register because she kicks so much ass. Of course I want the woman to be an actual character as well. I really wanted Hancock to join initially. Didn't like her at first but she grew on me after falling in love with Luffy and I saw great and fun comedic potential in it and apart from that, she was a melee fighter that gets into fisticuffs. I found her fun, kick-ass and she was a Shickibukai to boot so that was interesting (of course I quickly gave that up due to the lack of deep interactions during the war).
Now to be fair, One Piece is fairly okay when it comes to my little peeve about Shonen. A little too slanted to the male side but quite okay on the whole for the action scenes and power ranking of characters (I have no complaints about the stuff in flashbacks or what happens to poor civilians though, that sort of stuff is another thing entirely). I just really want a fun, hyper tomboy in the crew, someone like Bellemere would be perfect.
@RobbyBevard:
Marguerette actually had some semblance of a chance for a while, for a variety of reasons, but she was so quickly overshadowed by Boa that it was moot within a couple chapters of her appearing.
And yet some people were going about her joining right up until before the timeskip after Luffy went back to AL.
Well the fact that she DIDN'T get a title card went a long way in hinting she'd just be a minor character.