>>132875398Luffy already said he wanted ten people for his crew, and Oda has said he wants the Straw Hats to be as large as a soccer team (11).
In addition, it was confirmed that Blackbeard currently has 10 members of his own main crew, foreshadowing each one will be an equivalent to the Straw Hats (Burgess to Franky, Shiliew to Zoro, Laffitte to Nami, Van Augur to Usopp, Doc Q to Chopper, etc).
Jimbei will likely join by the time they start taking on the emperors, so all they need is one more crew member. It can be assumed at this point it'll be someone with a huge role in the story of the series as a whole, perhaps even have a connection to the origin of the Devil Fruit or the Lost Age of Pirates.
