A lot of OP fans, myself included do not think that anyone from this current arc are gonna join the crew. While there has been A LOT of discussion on exactly who will join due to the amount of new characters in this arc and then number that have interacted with the SH and Luffy especially.
Going with the assumption that no one will join from this arc, I was thinking when will someone join? There is 2 more members left, if you go with Luffy wanted 10 members besides himself, and Oda said somewhere that they will join successively. So if that is true I can't imagine the crew members coming in late and getting very little amount of interaction on the crew itself. That makes it seem to me that they will join realitively soon.
Jinbei is gonna join pretty much guareteed so if Jinbei joins when will he join? I have said this earlier in a blog that I think that he will join either on the way to Zo because of his cover story ending and the iminent Big Mom conflict or somewhere during or immediatly after Wano. So if that happens then someone will have to join in either the same arc or in the immediatly succeding arc. This leads me to believe that someone from Zou or Wano will join which gives me the vibe that either Kine'mon will join (which i don't think will happen or want to happen) or a minkman will join. On top of that I doubt we will get a 3rd swordsman no matter how different the style is.
The reason i think a minkman will join is the racial diversity that the SH have. They have a skeleton, a cyborg, a reindeer/human, fishman, and humans. The only other races i see in the OP universe is Giants, dwarfs, a Centaur, the longleng tribe and the longarm tribe. I don't see the need for another leg based fighter on the crew so i could see a longarm tribesmen. Since we have already gone thru an arc full of centaurs i don't think that is gonna happen, samsies with dwarves, and if we somehow run into Elbaf I could see a giant joining though how he would get on the boat is besides me. The one i think will join is a minkman because of the name of Zo and we have seen a few supposed minkmen throughout the series (Bepo and Pekoms come to mind). Another thing that could potenially fit is that the minkman could be some type of brown furred animal or an elephant minkman giving him/her a color advantage in that one color theory of SH recruits. Also the elepahnt one amkes the Zo make more sense.
Another possibility that I have thought of is when JInbei joins then Wadatsumi will join along with him. This solves the problem that a giant could get on the boat since he can breathe underwater. Also this helps out the San Juan Wolf thingy in the final battle against the BB pirates. I don't see this happening but it is a small possibility. This would also break the hope of a female joining and the MFMM thingy in each sea.