Remimd me, case I skipped almost entire Wano, from chapter 1996 till now, did she said that she want join crew and Luffy accepted it? Even if she said that she need mas*urbate or *erk off before joining. It is obvious that she will join before jorney to Raftel. While before this jorney we need three more arcs: Last island of Grand Line; Elbaf, Vegapank. So we basically now on Vega so we need now two more arcs and then Yamato could join crew. It's same as Jinbei who promised to join crew after settling things. Just wait and you will see side story with Yamato in Wano adventure, like it happened with Jinbei