Lately, a lot of people from the OP Fandom have been insinuating that there will be a new Straw Hat crewmember. The newest Strawhat Member, Jimbei(I like this name better), officially joined during the Whole Cake Island arc but wasn't properly apart of the group until the middle of Wano-Kuni. I'm stoked that he joined because he was crazy good during Impel Down/Marineford arcs and I thoroughly enjoy his appearances throughout the series. Apologies for the side-banter but I got to show some love for this fish.
Anyways, the fandom are theorizing Yamato, Otama, Momo, and Carrot as the newest Straw Hat. Each character have pretty good reasons to become Strawhats but I think that these are purposely red-herring like Franky. If anyone remember Water 7, it was very clear that a Shipwright was explicitly stated to join and the introduction of these shipwrights played with the expectations of the reader. At the time, I already knew Franky was a Strawhat but I can clearly see that the story was presented in a way that the other Shipwrights were still possible as a Strawhat member. I think that if their will be a new Strawhat, It has to be a character that plays a specific position as a Pirate.
Clearly, Oda has specific positions for each Strawhat except for Zoro(some say First Mate/Vice Captain but that hasn't been outright stated by the author though certain characters have stated it). Take Jimbei for example, who has been stated to be the "Helmsman" of the Strawhat even though his role as such has been lackluster and more forced than natural given his former occupation as a Warlord of the Sea. If there was a Pirate role to be filled, I can only think of a Cabinboy. The rest of the fandom thinks this and I am incline to agree.
Now that I am done with the exposition, The newest member that I think is probable is Toko.
Now Toko has certain ties that can be explored further and has potential to be an interesting addition to the crew. For one, she is technically apart of the Shimotsuki Family even if she isn't related by blood. The Shimotsuki is famed for having The God of the Blade(Ryuma) as an ancestor. As of this story, there is only one surviving blood family member but hasn't been seen since East Blue. One of the core themes of One Piece is that bond is stronger than blood and Toko fits in well with that. Not only that, but Zoro has ties with the Shimotsuki Family with Yasuie(Toko adopted father),Kuina(Childhood Friend), Kozaburo(Childhood "Friend") and Koushiro(Zoro's Sensei). Not only that, Zoro was temporally the wielder of Shusui(The Sword of Ryuma). That's way too many connection for one character to have for a Family that hasn't been elaborated on until Wano-Kuni.
Another factor that could play into the story is that Toko is a victim of the SMILE Fruit. The fruits are the failed experiment to replicate the powers of the Zoan Devil Fruits. If you get a bad batch, you are forced to smile like the fucking Joker. I believe that the SMILE Fruit will play a key role after Wano-Kuni and will be explored alongside Vegapunk, a character that is a key player in the world of One Piece. If there was to be a character that represents the SMILE Fruit, Toko is a strong candidate.
Now the reason why I became more confident with this theory is because of the latest chapters. If you aren't caught up too bad. What business do you have reading after I said Massive Spoilers. Anyways, Zoro has defeated King(Kaido's right hand man) and has succumb to his injuries. We know this because Zoro sees a version of the Grim Reaper, meaning that he is on the verge of death. Now for anyone that knows, Zoro got BTFO by Kaido and is currently on drugs to help him go up against King. So he might just be hallucinating but that hasn't been stated as such. I believe that this is the first canonical appearance of the Grim Reaper and that Zoro will explore the One Piece version of the Underworld. This is a high stakes gamble on my behalf because I will look like a moronic buffoon but this plot thread will raise an opportunity for Zoro to meet the dead Shimotsukis, especially Yasuie who is the adopted father of Toko. After this chance encounter, It would be quite a setup to have the Zoro/Shimotsuki payoff in such a big way. This in the form of Toko becoming a Cabinboy and a trainee of Zoro. Plus, it only seems right that Zoro become the sensei for a new generation of Swordsman and play with his belief that gender doesn't matter to become the World's Greatest Swordsman. It would also create a New Trio(swordwielders) within the crew that Oda likes having fun with. All great things come in three otherwise Zoro wouldn't be a three sword style user.
This theory doesn't really have a lot of ground to stand on and flimsy at best but this has been bugging me for quite a while and it's interesting to shake things up for who may or may not be the next Strawhat. Hell, there might not be one and people should be be content with who we have.