I actually have had the opposite: the more I read the more I’m convinced that they won’t join; Yamato in particular.
Tama’s the biggest maybe because she wanted to be a ninja to join Ace, but a lot more emphasis has been placed on her desire to get a decent meal every day. That can accomplished by either staying in Wano once liberated or joining the crew. But I’m personally leaning more towards her staying.
Momo’s entire journey however has been about him becoming shogun of Wano. It’s what he and the main cast have been working towards. Having already fulfilled Oden’s wish to see the world after traveling with the Straw Hats, and him becoming the symbol of Wano’s future “dawn” over the course of the arc, the only conceivable reason he might be motivated continue to do so would be if the arc made a hard swerve in its trajectory where it ends with Momo deciding not to open Wano before seeing what convinced Oden to do so Laugh Tale first. Which would be a HUGE slap in the face to not only Momo’s coming of age story when his biggest character flaw is him being cripplingly risk averse, but the entire theme of “fortune favors the bold” that the Wano arc is built upon. Even if the theories about Sukiyaki being alive are true, Momo leaving would still signify character regression rather than growth.
As for Yamato, the biggest reasons I don‘t see her joining are her overall placement in the story, the way her characterization has been presented, and her utter lack of connection with the main stays. For one, Oda has never introduced a crew member in the literal third act of their story - they’ve always been integrated into the plot in an arc that specifically revolves around them, or several arcs before their own personal arc. And for good reason: the new characters need time to build a rapport with the crew and establish their dynamic before they become part of the main cast, without that essential transitional period there’s no glue to bring them together. If Yamato is truly supposed to join, it doesn’t make a lick of sense to have the vast majority of her screen time be dedicated to her bonding with Momo, who is in all likelihood remaining in Wano, while the rest of the main cast doesn’t even know she exists. Oda even seems to go out of his way to keep her apart from the crew, with one scene where she leaves the room only a handful of pages before the crew does a large group shot, so trying to integrate her now can only feel forced. What, is she going to start trying to bond with the Straw Hats while they’re in the middle of frantically giving Zoro CPR?
For another, Yamato’s character arc has also been occurring independently of the crew and as a result is practically finished, which means once Wano ends there isn’t much else to build off of from there, which means there isn’t an organic avenue to have another Yamato-centric arc for the others to get behind, which means she’d have to intrude on an otherwise unrelated story arc as a substitute. Does anyone really want to see highly anticipated arcs like Elbaf get turned into The Yamato Hour because she has to awkwardly insert herself into everyone else’s arcs she’d otherwise have no business having a part in? Plus, considering how heavily she’s tied to Oden, I don’t think she’d really add anything to the crew’s overall dynamic anyways. The only role she’d have in the rest of the story would be telling the audience whether or not the things the Straw Hats are doing align with what she’s already read, which would get old real fast.
Finally, Yamato’s whole “I wanna be Oden” because she associates Oden with the freedom and acceptance she desires feels set up in such a way that the thematic trajectory for her would be to move away from copying Oden and forge her own future. In the scenes where she talks to or about Luffy, its always exclusively in the context of comparing him to Ace and Roger; she even says something along the lines of “logic dictates”/“following the proper logic” as an her main reason for asking Luffy for a ride out sea because it matches up with what Oden did and because Luffy reminds her of Ace. Even excluding that taking on someone else’s identity rather than embracing her own is kinda working against her own ideals (and is at this point futile since all the adventures Oden was shown to have that inspired Yamato are all ones that are far behind the Straw Hats) Luffy just isn’t going to appreciate being treated as either a replacement goldfish Ace or as a Roger stand-in to compliment her Oden LARP. It just doesn’t make sense to reward her eventually moving away from Oden, her symbol of freedom, by her relegated to only doing things exactly like Oden.
