@Gia:
Hey it could totally happen:p
My thought in it is that Jinbe and Yamato would join, but then Carrot would pull off the same stowaway stunt before WCI and mirror the exact moment Inu/Neko did twice to Oden lol. Kind of very in-character for her
Carrot stowing away is a distinct possibility, though I personally hope her joining would be more above board: her asking, him asking, them asking at the same time maybe.
And sure, Yamato joining could happen. But after ten years of waiting for Jinbe and three years on the Carrot bandwagon, Yamato's entrance seems way too blunt to me. Yeah, on paper he/she seems great, and had he/she had been woven into the story properly like Oda's clearly capable of, instead of on fast forward, I might have been down for him/her. But it feels waaay too easy here.
Tin foil hat talking, but I get the feeling Oda wanted to set up the idea of the tenth person joining right after Jinbe, so he postponed Jinbe's toast and had Yamato put the idea out in the open. But Carrot's the one he introduced years ago, set up on the adventure relatively early and ingrained into the group's dynamics. She's been in the cards a long time now, and if Oda was going to introduce the last member and give them time to acclimate, that was just about the right time frame to do it. Too soon and Jinbe's absence would be even more palpable. Too late, like the climax of Wano, and their place doesn't feel earned.
In my eyes, the crew sketches in Data Book Green are the Rosetta Stone to this discussion. I fully believe Oda had some semblance of Jinbe and the tenth person planned out from the beginning, hence why they were erased and there were only eight plus Luffy. If Yamato was actually the tenth, he/she would have had some presence in Oda's plans from all the way back then, and he wouldn't have waited this long to get him/her into the story. Yamato is a means to an end, not the final result.