Hum, maybe Yamato will get promoted to Okanban. It could be anything really.
The weird thing is why it would be "confusing" and why it almost seems like the announcement of the alliance needs to formally happen first. It either sounds like Yamato is central to the alliance (marriage or being their son) or BM/Kaido are about to do something Rocks related (recruit the former members, therefore leave Wano?) and Yamato is central to maintaining the current alliance at Wano?
The 2nd option sounds outlandish (since Kaido is built up as the arc villain), but we didn't find out about Katakuri until midway into WCI...so now I'm not sure lol. Obviously revolves around the idea that Yamato is powerful/a villain.
The only reason I bring this up is Oda (through Sengoku), talks about Rocks like some immense threat that may pool over beyond Wano. If Kaido/BM go down here, then I feel like it was a non-existent world issue if it's all resolved at Wano.
Like, I'm imagining 3 major threats. Blackbeard and whatever he is doing, the WG and their plans, then BM/Kaido further forming an alliance with their old comrades, and leading to whatever Sengoku was believing will haopen. Shit is both world ending and scary. Idk, I'd like it and also hate it at the same time because that means beyond Wano, all 4 Yonko will still be around lol. But if both are done at Wano, it kind of defeats the purpose of Sengoku talking about them like they will be a persistent problem.
Basically I can see both crews going entirely down this arc, but "Rocks" living on and getting worse.