To be honest I think none of the people in the vote will join at least not now.
Boa has her island she needs to take care of, Jimbei will have his hands full with defending his island after Whitebeards death, Perona wants to lead a comfortable life with many servants, Sir/Lady Crocodile has his/her own dreams and is probably to proud to be under the command of Luffy, Boa Mancock will try to get revenge for being turned into a man, Cindry is death, Spandams shoes are still stuck with Spandam, Montblanc Norland is death and Luffy hasn't had met Dr. Black Beard yet.
The first thing the straw hats have to do is returning to Sabaody Archipelago.
If they should really get a new member it would be either a fishman or a cat.
The thousand sunny must be invested with rats by the time the SH reach it.