Only thing I want to throw out there (and trust me, I'm going to preface this by the simple fact that I've been a Yamato supporter over Carrot since the beginning), is that Carrot's scene is pretty weird.
It doesn't actually end with her accepting, and what's weird is that Pedro's will really had to do with supporting the future PK at the time and boarding his ship (and nothing to do with ruling Zou). Yes, what it might just mean is that Carrot will be in charge of the Zou group and Zunisha to open Wano's borders and eventually unleash Pluton (unless something else opens it).
And yes, Yamato is 100% joining, but I've also thrown out the "possible" idea she acts as a stowaway, just like she did before WCI, and just like the Mink kings did with WB and Roger. Its an ongoing gag, and I really wouldn't be surprised if Oda threw her in last minute and this is really a triple join.
Again, i personally doubt it, but it's not surprising I'd say. What really kills it is if Carrot doesn't pull this stunt and they "kanpai" with only Jinbe/Yamato (which ofc, I agree 11 should just be the number if it's meant to match Blackbeard at least), which is obviously more likely to happen.
We'll see I guess lol.