I've got Carrot joining at a 95% chance. Not because I think she is currently developed enough to join as she is, but because it could only possibly be her.
There are many convincing arguments to suggest that Wano is the last possible chance to pick up a new crew member. And as of now, there's no one that shows even slightly close to the same amount of potential as Carrot in joining. So much so that headcanon is required to explain a reason in the story as to why she wouldn't just ask to join the crew at the end of the arc and be accepted. Whereas headcanon is required to explain why other characters will randomly join.
Not to mention the entire unorthodox nature of Carrot's character.
You look at her design, personality, fighting style, strength, etc. Any of these are at a perfect level to mesh into the crew.
Carrot's all but confirmed to me. Just waiting to see how it happens. I'm not looking for even more clues to consider things. More than enough has already been provided to indicate she will join at some point. Not because of personal liking for the character, but looking at the actual facts in the story.