Holy shit, I just realized something after seeing King and Kaido's flashback...
Kaido....
Thought he could become Joy Boy.....
When King asked him if he could change the World, Kaido replied that he was the only one who could....
Joyboy is meant to be the one who changes the World, as indicated with his promise to the Fishman, hundreds of years ago....
When Kaido told Luffy "You can't become Joyboy either" he wasn't talking about him looking for someone to become Joyboy like many were speculating. He was referring to himself wanting to become Joyboy, but being unable to.
This might be a huge clue as to what drove Kaido to become suicidal, and turned him into to what he has become today. This also explains why he desperately wants to destroy the World, because in Norse Mythology, the only way to rebuild the World anew was to destroy it, and that's what happens during Ragnarok. The World gets destroyed is reborn anew.
Kaido wants to destroy the World, in order to "change it" and thus proves that he truly is "Joyboy".
Oda has been fucking telling us this the whole time with the whole "Yamato/I am Oden" schtick, because at one point in Kaido's life he believed he was Joyboy.... It explains why Kaido supports Yamato by referring to her as his son, but also he doesn't support her for claiming to be Oden, because he was the same exact way when he was younger, and no matter how much he claimed it, it never came to pass.
Yamato is claiming to be Oden, and desperately wants to change Wano...
Meanwhile when Kaido was younger, he was claiming to be Joyboy, and desperately wanted to change the World....
Fuck me, if this is the route you're going with Oda, you're a genius.... I might have to make this post a thread when the chapter drops...