At the moment, Luffy seems to be ahead of every supernova, the only one capable of taking on an emperor on his own.
Now that Kaido and Big Mom have both been defeated, what happens? Luffy is already considered the Fifth Emperor so we can assume that he will replace Kaido as Yonko. But who will take the place of Big Mom as the Yonko?
Unlike Whitebeard who had allies and lands that were under his protection, Kaido has an army and a state set to return under the supervision of the Kozuki Clan. What will happen to his army after the battle? I think Eustass Kid might take over, perhaps inadvertently inspiring the Kaido Pirates to go after him or something. Otherwise I don’t see where his character is going other than following Luffy’s lead, and it was written specifically as someone that Luffy will compete with in the future, whether in a contest or outright…
Now I don’t know anything about the Big Mom Pirates, but I’m pretty sure that all those allies that Kaido joined won’t disappear from the story, and I doubt they’ll join Luffy. Blackbeard might jump into the frame and take over but I’d prefer Kid to gain some leverage…
Being a child Yonko in the future is highly probable given that he’s one of the most powerful pirates in the same generation (and the next generation) with Luffy and I imagine he’s someone you can consider a “balance agent” when it comes to power and influence.
Then what about the Trafalgar Law?
Law is undoubtedly one of the strongest pirates with a truly amazing Devil Fruit ability, but I don’t see him getting that Yonko title anytime soon or even at all. He is a perfect fit as Luffy’s ally.
* theory Choir 1012