At this point I just want Oda to finally recruit Vivi back instead of some newly-added character, because I have strong doubts that he wouldn't add the ex-crewmate to the final journey to Laugh Tale. The only other candidate I'd accept would be Carrot; not because I enjoy her character, which I particularly don't, but because narrative-wise I actually find it interesting for her to be an apprentice whose "dramatic past" happened during the current timeline. It kind of fits the idea of a newly added member that will truly shine after our crew no longer exists (beyond end of series) and is now experiencing the kind of events that the well-established, veteran crewmates lived in their pasts (I hope I explained myself properly).
But again, no Yamato, no Carrot: Vivi is the way and the perfect closing of the circle.