I believe it's disingenuous to still hold potential Nakama candidates to the same to the tee standards as members 1 through 8. Someone pointed out Jinbe for example.
If you re read Fishman Island's flashback, Jinbe is a mere witness to the lives of Otohime and Tiger, who he's the most connected to in that arc, but can we honestly say his connection was any stronger than say Arlong? I don't think so.
Yet, he still joined. Also, Jinbe said he was joining since FI arc and we still have yet to get a str8 forward dream from him outside of vague references to fighting for fishman/merfolk freedom through following Luffy and helping acheive his dream as PK. But he joined anyway, but I regress on this for now.
Bonney not being planned ahead of time shouldn't disqualify her anymore than it did Franky or Robin. Who weren't early concepts either. Or how Ussop, Brook and Chopper are vastly different than their original concepts. Zoro was originally apart of Buggy's crew, and maybe the plan was to always have him switch sides, who knows except Oda. But from the old sketches we know who was always meant to be strawhats.
The original 4 from East Blue. Brook, Chopper and Jinbe. Everyone else was either merged into existing characters or cast to the void of Oda's imagination.
While I do agree that, because of what happened with Yamato, there's no guarantee Bonney joins even if her and Luffy are attached to the hip for the rest of this arc, and she actually shows interest in joining. BUT let's not pretend because Kuma has been the focus of this flashback, it negates Bonney's own trauma and development in these situations concerning major key factors.
Her priority subplanted even Ginny's In the story, who was indirectly responsible for God Valley. Yamato had even less going for them outside of claiming they'd leave with Luffy, we got alittle information about her traumatic childhood from her tough love under Kaido, and her being a Oden Stan. Who's flashback was ALL about him with the Scabbards as the closest runner ups.
Bonney is already connected to Celestial Dragons, World Government agents, scientists, Marines and literally raised on Nika as a religion by Kuma himself, who the crew viewed as an enemy until relatively recently in story wise.
Her personal story arc has echoes of Franky, Sanji, and Robin. Her arc holds emotional weight and has ties to the wider issues plaguing the story.
These facts shouldn't be ignored.