@Natsu:
I've been saying the crew gets a cabin boy since the time skip, and calling Momo since PH. As we've learned more about him, I've only become more convinced.
- He has to learn how to read poneglyph (Robin)
- Doesn't feel like he's ready to weild his dad's sword (Zoro)
- Would need a trusted retainer/body guard (Carrot also joins)
- Has great crew dynamics
I think once they beat Kaido, Hiyori, the scabbards, and the Yakuza will run Wano while Momo joins a pirate crew like his dad.
Been a long time since I've been here, was looking through this thread for good theories about the next/final crewmate. Your post really struck me and I found it very convincing, but the more I think about it, the more I also start doubting aspects of it. I'd never considered that Momo would want to learn the Poneglyphs and, as it stands, Robin is really the only one who can teach him. On the other hand, though.. Does he really need to learn it? Hear me out here: basically everyone either already believes or will fully believe that Luffy will fulfil Roger's (and Oden's) wills (we clearly saw that with Pedro's sacrifice in WCI). So assuming that everyone has complete faith in the Straw Hats to take the Poneglyphs to the end, what use will there be for them after that?
I'm definitely not saying that this is an argument against Momo, I'm just thinking how I don't know if he necessarily needs to learn about them now. If he wants that knowledge later just for the sake of preserving the knowledge, he could always learn it after everything in the series is said and done. I still think you make a good argument and it seems very possible, just maybe there isn't as much of a need for point 1 right now.
Also @ point 3, with Carrot also joining, that would bring the amount of crewmates up to 12, which is one more than what the concensus always held. I don't know if over my years of absence people have convincingly argued that 12 members is very possible, but I remember people being dead-set on the final figure of 11 because
1. Luffy said at the very beginning he wanted 10 crewmates, which was by and large interpreted as 10 people aside from himself
2. Blackbeard's crew currently has 10 captains and him as Commodore, so unless he gets one extra (which is possible I guess) the number wouldn't add up to give everyone a 1v1 at the end
3. Oda loves football so it'd be nice in concept to have the same number as a football team
So I don't know about 2 more people joining.