In the first place Lilin doesn't really have automatic right to custody of any of her children and is only able to do it simply because all of her husbands or is lovers? lolz have been powerless before her, whereas with Kaidou that isn't really the case. That said it's an interesting possibility regardless ^^.
The whole point of the alliance is for both Kaidou and Lilin to dominate the world and then the two plan to fight out between themselves to reign supreme so I don't think it makes sense for them to delegate that responsibility to Yamato even more so from Lilin's perspective. Moreover what could possibly be more important for the two than world domination atm?
If this were the case Kaidou wouldn't have needed the SMILE army from Doffy and Caesar in the first place and there'd have been no reason for him to ally with Lilin if he's always had a weapon of such magnitude in his possession.
Yh guess we'd see in a few chapters ^^. That is, if the party gets to even proceed that far...lolz
Part of me has this "eerie" feeling, and its a small one but I've been thinking about it for a while, that Kaido/Big Mom are meant to further propel a Rocks plot that is beyond Wano. Sengoku and Garp talk about Rocks like its about to become a massive threat (through Oda's words). I also know that Kaido/BM are considered a worse threat than the original crew seemingly, but its the WAY Garp/Sengoku talk about Rocks that gets me. To me, it strikes weird that a lot about Rocks isn't even a part of Wano save for Kaido/Linlin:
- Garp himself
- Weevil/Bakkin
- Former Rocks Pirates (only teased by Sengoku)
- Former Roger Pirates
- The overall goal of Rocks was unknown, but had to do with God Valley.
I know the above sounds wacky on paper, because Wano has been built up for years as taking down a Yonko, but I'm at this point where I don't even see how Luffy is going to win here lol, let alone have to deal with 2 Yonko. Sure, Neko may bring enough reasonable reinforcements (the former WB pirates especially) and that may definitely help, but Luffy himself lost immediately to Kaido in one hit. That never happened before this arc, and I'm not sure how that gap is supposed to be closed going from Katakuri to Kaido. I'm sure Oda could find a way though.
We still honestly don't know why Kaido had an affinity for Wano in the first place, or what questions he needed to ask the Scabbards, or even his past, and I'm also not evensure how the whole Rocks goal ties into this, it was only recently introduced in 2 other chapters and teased by Marco. Weevil now has to deal with not being a Shichibukai and we have no idea how that factors into his character, but Bakkin allegedly tied to Rocks through Marco's comments about her. Its just like, if we have characters outside of Wano that are part of this Rocks plot, is the Rocks plot even finishing on Wano?
The above is the ONLY reason why I'm guessing Yamato may be important in actually "uniting" their two crews (be it some power he has or relationship to both BM/Kaido) and could serve to be the arc villain for Luffy.
But yes, we really need to see what Yamato looks like. If he's a kid or he's good, then Kaido is totally going down this arc, regardless (being Luffy's main battle most likely somehow). If he's bad and looks to serve as Luffy's foil.....then I'm afraid that BM/Kaido may not go down this arc and live serve a bigger plot, just like Blackbeard and Shanks seem to be doing eventually. These are the strongest pirates in the world, so I could see their characters surviving beyond this point.
Also a big issue I have with Luffy winning against a Yonko here is how it really lowers the threats of Akainu, Blackbeard and other Non-Yonko/Admiral threats (Vegapunk/SSG if they are a personal threat to Luffy). Not defeating Kaido/BM here, but allowing Luffy to take out their crews (and still fight someone stronger than a Yonko commander) here with his alliance still keeps Luffy the "underdog" for a longer time if you know what I mean.
Idk, I know I'm one of the few that shares this sentiment, but we'll see.