So i've been a long time lurker on here, and just have a few thoughts on the next nakama thing.
In East Blue, Luffy picked up 4 crewmates, then picked up 4 more in Paradise. It would be pretty reasonable to assume that he will pick up 4 more in the New World. So far, we've only gotten 2 characters that have received the full flashback/full arc treatment: Jimbei and Law. Both had their own pirate crews to start with, and while Jimbei has agreed to part with his and join the Strawhats, he hasn't traveled with them. On the other hand, Law has traveled with them but has not agreed to part with his crew. Law seems to have complete faith in the strawhats, and is also a D, so it's not unreasonable that he should have interest in the endgame beyond being part of the grand fleet to help in giant brawls. The main question with him is whether he'd be willing to depart from the Heart Pirates. Maybe the end of Wano will provide them a home of sorts? I know, I know, he's a doctor, chopper's a doctor, he's a shichibukai, jimbei's one too, etc. However, this is the Pirate King's crew. They need some powerhouses to fill out their ranks.
As for the 2 remaining spots, the most obvious choices seem to be Carrot and Kinemon. Most people have completely dismissed him as an option, and i'm not sure why. He's in his prime, has a 2 sword style, funky personality, and established crew interactions,e tc. The only thing holding him back seems to be his role as a retainer to momonosuke, and that he has a wife, Otsuru. The reason I think he may join them on their journey is that Momo will want to fulfill his father's wishes (as will Kinemon) of opening Wano's borders. It makes sense to have someone travel with the strawhats to see the world, and it sure as heck won't be Momo, Vivi-style. So he'll send his most loyal retainer, his wife'll be like, it's been 20 years already, i'm a different person, what's a few more years, it's nice to know you're alive, blah blah blah. His other retainers aren't quite as established, too old, or too weird (raizo and kanjuro are just bananas characters).
Carrot is an interesting case. She's been highlighted sporadically, traveled with the crew, and has shown a badass powerup. There are no other mink candidates since pedro died, and since the strawhats are so freakin' diverse, they could probably use a mink. The main detractor with her is that she hasn't seemed…necessary? She hasn't driven the plot at all really, she was just there and decided to take the trip. On the other hand, she can handle herself, has interacted with the crew in new and interesting ways, and yes...i'm buying the lookout thing. These two aren't quite as powerful as Law and Jimbei, but that's good. Can't have everyone be a monster. Unlike previous crew members, their dreams/dead mentors are a bit more roundabout, but they still exist. Opening Wano/Pedro's will, Oden and Pedro. We've never seen the tragic thing happen so currently for our nakama prospects. Oden, in Kinemon's mind, was just recently killed, while Pedro JUST died. So the format is different.
Or we can meet some other characters down the road, but man...we're close to the climax here, it'd be weird. anyhoot, just some thoughts.