To me its really about tying Yamato into the story and making her relevant. We only knew Ace went to Onigashima because she mentions they had a relationship of some kind. What I'm hoping for is that a Kaido flashback just sort of covers all of it:
- Starts with Kaido as a kid/dragon/whatever, gets adopted by Rocks or something
- Meets Big Mom/Whitebeard/Shiki, we see snippets of the God Valley incident (assuming Oda doesnt want to reveal everything about that incident yet)
- Group disbands. Big Mom and Kaido have some additional relationship (he owes her for some reason). Kaido sent to Impel Down.
- King the former Warden, befriends him, is sent to Punk Hazard for giant experimentation. King accompanies him there. Queen, a Vegapunk scientist, also befriends him.
- All 3 break out of Punk Hazard with the other failed experiments (the Numbers). Incident is covered up.
- Time goes on, Kaido has Yamato with someone, encounters a young Jack, takes over Wano, beats into submission Sasaki, WsW, Black Maria, etc.
- Ace arrives at Wano, encounters Yamato, they are close. For some reason Ace leaves and doesn't return (this is what I dont get)
- We see plenty of scenes where Yamato has a terrible relationship with Kaido. We see a ton of character motivations from Yamato and growth.
- Back to present
Not sure but I hope its all one consolidated flashback, unless the Ace stuff is only meant to last a chapter or 2 with Yamato.
Edit:
@Bounty obviously what I'm saying above is all guesswork and bs, totally don't know anything about Kaido's past or adamant on that yet