Hey I know it's been long, but what the hell. I just wanted to say my opinion, hope u don't mind

Everyone keeps saying a new nakama will join because Luffy wanted 10 nakamas... except, well, he already
has 10 nakamas! If ou think about it, they remained as Vivi's nakamas, right? Counting her, it makes 10, so goodbye to the, as sanji would say, shitty rumour!! (I wished she came back through...)
However, people keep pointing out one of these ppl will join: Hancock, Perona, Margaret, Jinbei or Bon Clay (If he's alive, of course). However, in order to join the SH the new members need the following:
-A position in the ship (Not esential, Robin or Usopp aren't esential to the crew if u think about it)
-A skill at which you excel (Or simply be a Devil Fruit user)
-A traumatic and horrible past.
-A special dream they wish to acomplish by navigating with the SH.
If you think about it, Hancock has more chances of getting in, being the only one that has a terrible past (her days of slavery)... yet there isn't exactly a position for her in the crew, given that she's the captain of her tripulation (through Zoro doesn't have a specific position either...) And about her dream, it could be either marry Luffy or taking revenge on the Tenryuubito, take your pick. Another chance is Margaret, who desires to see the world outside Amazon Lily and has been shown to possess an unique talent for sewing and creating clothes. But, unlike Hancock, she doesn't have a sad past, and every crewmember has one!
I doubt Perona or Jinbei can join, they will probably remain as allies, like Paulie from Water 7 or Conis from Skypiea.
If Bon Clay is alive, he would probably join the straw hats, or at least Luffy would try to convince him to do so, given that he saved his life in more than one ocassion. Not sure if he would join or not, but I would love to see him interact with the crew, specially Robin, Sanji, Nami and Franky. So, I guess Bon Clay is my pick, in case he's still alive.