I agree that the last chapter had an anti-climatic ending for Zoro's character. If Zoro scarring Kaido was going to be the climax of his character arc in Wano, why have it be overshadowed by Luffy unlocking advanced CoC immediately afterwards? Given where we are right now, it feels far too early for Zoro to sit the rest of the arc out. We still don't have a match up for Sanji, nor do we have any idea as to the intentions of the remaining Big Mom Pirates.
I think Enma has to become black in Wano. Why else would Oda introduce the concept of an almost black blade?
His sword from Kuma will presumably turn black upon becoming WSS, as this links the "will" of the blade with its blackening. For the same to occur for Enma, the only possibility is repeating Oden's feat or surpassing it. Given that Zoro just scarred Kaido, that leaves killing Kaido as the only remaining possibility. Could Enma turn black upon defeating Smoothie? Sure, but it would ruin so many parallels and narrative themes that have been carefully setup over the past decade.
First, we have Ryuma (who shares many parallels to Zoro), the samurai who wielded a black blade and slayed a Western Dragon. Zoro then slays a Western Dragon with said blade. Then we have Oden (who also shares many parellels to Zoro), a samurai who almost killed an Eastern Dragon with an almost black black. Zoro then exchanges the black blade that killed a Western Dragon (twice) for an almost black blade that almost killed an Eastern Dragon. Zoro then states his desire to take the head of an Eastern Dragon and proceeds to fight said dragon shortly after. Furthermore, in case it wasn't too obvious (apparently it wasn't), Oda goes on to emphasize the theme of inherited will, in the specific context of swords, when we learn that in Wano samurais will pick up the blades of their fallen comrades so that their will lives on, even after death.
Over many years Oda has set up a carefully constructed narrative that incorporates swords and their blackening, dragons, and inherited will. The only logical ending to this narrative would be Zoro using Enma to kill Kaido and blackening the blade as a result. I would even argue that without having this ending in mind, an author would have been unable to write such a narrative into the story to begin with.
On top of all this, we have another narrative of Zoro becoming a legendary swordsman, whose "name will reach the heavens." Ryuma became the hero of Wano after beheading a dragon over the Flower Capital. Given that One Piece was originally supposed to be about the Straw Hats overcoming the Yonkos, and the introduction of Ryuma fairly early into the story, as well as the fact that Oda made Wano Zoro's ancestral home, we can assume that Oda intended to have the Straw Hats face off against Eastern Dragon in Wano from the onset of the story.
Thus, in 1999, it is not unlikely that already Oda knew the following:
- A swordsman from Wano was to be the second member of the crew
- That swordsman would have a desire to become a legendary figure and surpass all other swordsmen
- He would be following in the footsteps of another legendary swordsman who slayed a Western Dragon above the Flower Capital in Wano
- The Straw Hats would eventually face off against an Eastern Dragon in Wano
- That he desired to draw a dragon being beheaded (from commentary on "Monsters")
Is it possible that Oda created Kaido and Zoro independently from one another before deciding to link them together (via Wano and Ryuma)? Possibly, but I think the desire for a swordsmen beheading a dragon likely served as the basis for both characters, given his remarks on "Monsters."
Unless Zoro kills Kaido, Oda would be retconning two different (but interconnected) narratives that he has arguably been setting up over two decades. Not to mention the fact, that I have yet to hear a compelling alternative to kill Kaido (who really needs to die this arc), perhaps Luffy can just punch a giant hole in his head...