I really struggle to find one, because most guys that imo fit the Strawhat criteria are bound by something else. People often bring up all these different patterns but i think are forgetting the most important one that fits every member so far: Luffy is the one recruiting, you need Luffys approval. Perona for example is a popular choice, but Luffys reaction as she appeared with Zoro after the timeskip was "who is she?". Shes a dull and uninteresting character in Luffys eyes so why would he invite her?
Then there is Pudding who is someone Luffy liked at 1st, he foreshadowed her joining on Zou when he found out Sanji is getting married, but we havent seen any opinion or panelled reaction from him on her since she told him that Sanji will die, so even though she started off with lots of potential, Oda quickly removed her from the discussion (should i say for now?).
With Momo he has already a bond, he constantly challenges him and helps him grow, but hes still just a kid and heir to the Wano shogunate, so thats 2 things eliminating him even though hes practically already a "nakama". Kinemon seemingly fits the best but why draw a wife for him that hasnt seen him in 20 years if he was to come along? Hes been around the whole time in the New World, Oda could have easily skipped that detail if he planned him to join,
And my last point, Jinbe. He was such an impactful figure to Luffy and the story since 1st being mentioned in East Blue, he saved Luffys life more times now, he stood against admirals and yonko in Luffys name, he restored Luffys will to go on after Ace died, their bond was immense even before Luffy saw him again 2 years later. And after the timeskip their relationship grew even stronger. So how are you gonna top this then? Anyone who joins now wont have near as much clue about what Luffy has been through so far as the original 8 and Jinbe (unless its someone from pre TS like Bon Clay or Hancock, but such characters have been absent for a while). Does this narrow the choice or close the door, im not sure. Just hope that we wont get a disappointment like what Oda has written Carrot into so far.