I feel like if someone should join it's definately Yamato. Imagine if she was born from dragon egg from Roger ship?! Like it or not, but dragonkin race is something that could be called as great. It would be interesting to see Yamato from dragon race, who actually didn't became evil in the end, and different plot for story. Like Wano arc should became an end of dragon reing. Possibly that Yamato's mother was killed by Ryuma, so joining Yamato SH crew is really cool thing(if you forgot about her Oden thing). Yamato is unique, which is something that suits SH. Chopper was a raindeer with blue nose...he was always different and was aging different, than other animals. Franky is cyborg....the only one who could be compared to him is Kuma, and his plot eventually leading to Vegapank. Robin is maybe last human who could read ancient language from poneglyphs. Brook is litteraly skeleton, real undead man. So Yamato for real suits to join SH...I mean her ability to transform into dragon without DF is sick in good meaning. While Carrot...is nothing better than Pedro, yes she maybe have a bit different appearence, but that alone factor is not enought, to made her SH. We already have furry in the crew(chopper), while if Jinbei is a fishman with chinese lion-dog appearence, Carrot is just another mink. Yamato is dragon with red horns and possible hybrid dragon-human form, that will make her look like a demon or something like that.