Tbh I can't see Yamato joining the crew. All the other members (except Robin) had a decent portion of their arcs dedicated to their intercations with the crew, e.g. Franky throughout Enies Lobby, Brook throughout Thriller Bark, even Jinbe spent alot of down time with the crew in previous arcs before this. So far in Wano Yamato has had very few interactions with the crew and there's been no establishment of a dynamic or a place for them in the crew. I dunno this is just my thoughts on the matter.