This is from user reddit.com/user/viktorayy just for the props :D and cause I'm not claiming this as mine, even though it's been speculated... These are his/her words
After WCI or Wano, depending on if WCI directly moves into the Wano arc, the crew sets sail for a new adventure. Meanwhile, Carrot will have found that she actually likes the outside world quite a lot. It is fun and mysterious. So she stows away in the Thousand Sunny AGAIN and boom, they sort of have to take her now.
For anyone in support of the Snow Bunny theory, Carrot eating the Yuki Yuki no Mi in Nami's tangerine trees could happen before or after this event. So no big deal. IN FACT, I could come up with a funny scenario right now.
1. The crew finds out Carrot stowed away on the ship again.
2. They insist she shouldn't join them because it's dangerous or something.
3. Nami notices something wrong with her tangerine trees.
4. Carrot says she was hiding on the ship for a while, so she ate a bunch while she was waiting for the Straw Hats because they were orange like her beloved carrots.
5. Nami gets mad at her and demands x amount of beri from her, grabbing her arm.
6. Carrot says she doesn't have money because Minks use a different type of currency or they just don't have currency to begin with.
7. Carrot becomes nervous accidentally activating her snow power.
8. Nami suddenly feels her hand getting cold and is taken aback.
9. Carrot is also taken aback and loses control even more, causing it to snow.
10. Everyone is surprised and think Monet is back.
11. After x amount of time trying to search for a person who isn't there, they deduce Carrot is generating the snow and she ate a Devil Fruit.
12. Nami, being one of the smartest people in the crew, puts two and two together and realizes the fruit came from her tree and she could have made tons of money from the Devil Fruit.
13. Luffy is entranced by the snow bunny girl and demands more snow.
14.Carrot does so and says something like, "So can I join the crew?"
15. Luffy says, "Yeah, sure."
16. Nami is still ticked off and says that Carrot needs to pay her back before she leaves the ship anyways.
17. Boom new Straw Hat!
(Keep in mind this is just one of many scenarios that could happen if this theory turned out to be real, just giving an example of how it could work.)
If you support Jinbe joining, this could happen directly after him joining and the crew celebrating a new member. Oda DID say new crew members were going to join one after another. Now you can chalk that up to the Grand Fleet, but those guys aren't technically crew members, so I'd have to disagree.
If you support Pedro, no worries! This can still work. Pedro, if he's still alive by that time, had the foresight to realize Carrot would do this again, so he stowed away as well in a deeper part of the ship. He says he'll come along to keep her in check or something. So everyone wins! xD