Now that Luffy got the peak of his devil fruit power (awakening), it pretty much sealed the deal for Zoro to get the peak of his swords power (black blades) for anyone who still doubts it. Didn't happen against King as expected, remains only one relevant character it should happen against.
ACoC happened in this arc of all times and most would describe it as a wishful thinking to ever happen. Black blade atleast have some grounds for it to happen this arc.
Kaido is so OP it'll require Joyboy with the awakened most ridiculous devil fruit as well as a mighty samurai that is atleast as monstrous as Oden with black blade(s) to keep him down for good and to send him to the afterlife.