What's with the Momo for new nakama suggestions? He's 8yrs old. That is not a crewmate, that's a burden.
I think you forget the old tradition of sailing ships having a ship's boy. In my eyes Momo has disqualified himself already with his personality, but in principle I don't think there's anything which would speak against some sort of ship's boy.
so wait people actually think the dwarf princess is a candidate when we haven't even met her yet?!
and don't say it sounds like she has an interesting personality, what character in OP of any relevance doesn't! You might as well say every character will join….. oh wait
Thing is one of the main requirements for a new crewmember is that he or she does not fit within her established society. Nami and Usopp didn't fit in among the common villagers of their islands, Sanji didn't fit among with the deadbeat cooks, Chopper as a blue-nosed reindeer-man didn't fit either with humans or with reindeers, Robin was double-crossing Croco so she certainly didn't fit with him, Franky was too big for his gutter family, Brook had lost his comrades 50 years before and Jimbei as a former shichibukai has no real place in FI either. The only exception is Zoro who even without Luffy would be making his way to the top on his own- though he certainly would get lost on the way.
If you look at Leo's description of the dwarf princess, even without having seen her firsthand it seems that she does not really fit in among the dwarves. Unlike someone like Rebecca who has been tricked into being hated and who will certainly make the instant transformation from public enemy no. 1 into beloved princess/queen. Moreover as a dwarf Ma Cherie would certainly meet the weirdness factor of the SH.
Still you are correct that this hardly constitutes proof or even a solid clue that she will become the next member. It's just that at this point pretty much everyone will be brought up who is even remotely interesting and who doesn't disqualify him- or herself immediately.