Kin'emon, Momonosuke and Yamato are now locked in to join at a later date. We can now assume Vivi can offically join later based off the news about her father. The Strawhats would have Luffy, Zoro, Nami, Usopp, Sanji, Vivi, Chopper, Robin, Franky, Brook, Jinbe, Kin'emon, Momonosuke and Yamato.
By using the logic of there being no repeating letters of the alphabet at the start of the crew's first names, you could rationalise who will be next to join the crew. With the letters, B, C, F, J, K, L, M, N, R, S, U, V, Y and Z taken, this would leave A, D, E, G, H, I, O, P, Q, T, W and X remaining. With this being the Final Saga of One Piece the map to figuring who these letters symbolise can be deducted from the remaining plot points.
- A. Arbel has been waiting for Joy Boy. I Imagine he'll want to join to avenge the Lunarians.
- D. With Kin taking the K spot. Koby can no longer join as the "Marine". Drake joining would fulfil the debt he owes to Luffy.
- E. Enel. He's probably related to Uranus somehow.
- G. Sanji fed Gin when he was hungry once. Also possible tenth titanic captain of the BB pirates.
- H. When Luffy and crew overthrow the Celestial Dragons, I'd guess Hancock would want to join at this point in the story. Maybe she'll join sooner due to Cross Guild.
- I. We all want Bon Clay in the crew. However Ivankov starts with I and can join. Bon Clay would then replace Ivankov as Queen of Kamabakka Kingdom just like Carrot replaced Inu and Neko.
- O. Oars III or Onimaru seem like reasonable additions.
- P. Perona will most likely be involved with the Blackbeard arc since it involves Moria. She also knows Zoro and also has duality with Brook who can also turn into a ghost.
- Q and X. Q only has Doc Q and Queen. X only has Rocks D. Xebec as options to fill these letters.
- T. Tama could join. Maybe she'll force her ninja master to turn her into an adult like Momo.
- W. Wyper may have something to do with Uranus. Also has a possible connection to Arbel.