Please consider the following:
Bartolomeo has his own role as captain to think about, so why would he join? Despite his admiration for the Strawhats, there's no way he'd leave behind his own comrades. That's the impression I got when he's even starting to pat Bellamy on the back. He's a character that many likes, and obviously people would want him in the crew, but I don't think it's happening.
Both Momonosuke and Kin'emon are more like travelling buddies, just like Vivi was. They're already planning on going to Zou in the near future, so no, I don't see any of them joining the crew in this arc. As they've already stated, they want to go home to the country of Wano. Is it possible that they'll join the crew, even just one of them? Yes, but I highly doubt it.
Law has a crew of his own, and no, a flashback or two is not going to make someone join. We barely even saw a glimpse of his past, you know. Even Robin's past wasn't revealed before almost two-hundred chapters later. I'm even starting to believe that he'll retire as a pirate after this arc, after they beat Doflamingo.
Viola, mind you, is the princess of a country. She's the next to the throne, has a family to think about, and a country to care for. Why abandon all of that to be part of a pirate crew? It doesn't make sense to me, so fill me in if there's something I'm missing here. I just don't see her joining, despite her seemingly interest in Sanji, if there is any.
Rebecca shares the same reasons for not joining. She's a princess with a family, country, and home, to think about. She just found out that she has a father, and now she's just going to say 'bye-bye'? The same can be said about Kyros. I doubt any of them will leave Dressrosa for now.
Bellamy is my second choice, but I doubt he'll ever join the crew. His dream is basically to work under Doflamingo as an officer. Now, obviously, that dream has been crushed by Doflamingo himself. I find it more likely that Bellamy will join Bartolomeo's crew in the near future, considering how "well" they're getting along. Plus he seems to be holding unto some pride, so I don't know how he'd feel about joining someone else's crew.
Now, on to Sugar. She's been treated as a tool by the Donquixote family, she's had moments where she seems to regret her actions, and now she's going to wake up with plenty more memories in her tin can. All the people she's turned into toys, exept the ones who've died during the years, will turn back to humans. The memories of them will return to her. Obviously she's going to change in some way or another, unless she's experienced this kind of thing before. In my opinion, her chances of joining are sky high.
None of the dwarves have had much screen time up 'til now. This can be said about Sugar as well, but her role in this arc is by far more important than those of the dwarves. Plus I believe she has her reasons to be gone from the pages these past few chapters. Now, on to the dwarves, it's safe to say that they don't stand out, like, at all. There's Leo, but we barely see anything from him. This can change in the blink of an eye, though, but I doubt it.
Ucy is a bull, yet I still find him more likely to join than most characters we've met in Dressrosa.
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