Theory Zoro is the one who's going to kill Kaido.

Zoro is the one who's going to kill Kaido.
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Zoro is associated with a tiger (as well as a Shark in SBS)

Zoro is wearing a Dragon-style Kimono at a festival.. foreshadowing?

The dragon has Zoro fascinated, further alluding to the tiger and dragon mythology.

Japanese themed cover page has a tiger and dragon drawn, alluding to it having some sort of future relevance in One Piece's Japanese themed arc, Wano.
Stephen Paul's translation of Chapter 190
I can definitely see Zoro beheading Kaido.
He will definitely recreate the legend of slaying a dragon.

There is also an interesting comment that was made when Hiyori stated she would give Zoro enma in exchange for Shusui.
The comment was inherited will. We know Oden wanted to defeat Kaido and open the wano borders.
That is extra foreshadowing
The issue with Zoro killing Kaido is that he has really been presented as unimportant in the last few chapters and spotlight has been put on Luffy, Law and Kidd.

Oda hasn't created any personal conflict between Kaido and Zoro, he hasn't created any family ties with Zoro and Wano Kuni where he could have written revenge archetype with Zoro killing Kaido.

Before Odens flashback there was one plot point supporting Zoro damaging or even killing Kaido and that was Enma supposedly being the only sword to damage Kaido but that was quickly proven false in the flash back.

At this point all we have is loose parallels of Ryuma slaying the dragon to save Wano Kuni from it but issue with that is Zoro has even lost Shushui and so far Oda hasn't put any focus of Ryuma besides those words from Gyukimaru

And now we are in the starting point of the war, the strawhats are in Onigashima and next step is the plan coming into fruition.

The only plus point in Zoro killing Kaido is his sub plot with Hiyori but even in that sub plot Orochi was portrayed as main antagonist and not Kaido.

With all that why would Zoro kill Kaido?
I actually agree with a lot of this. The focus has clearly been on Luffy, Law and Kid. However I feel like it's an obvious red herring. Zoro killing Kaido will be a subversion of expectations. I do hope it gets more buildup and Zoro gets more spotlight in the coming chapters though..
The only way for Moriah to kill Kaido is to take his shadow and leave him in the sun.
Aside from there being better ways to end the WSC, Moriah would have to dare show up in Wano in the first place...
They would rather come up with a nonsensical theory about Moria killing Kaido and appeal to ignorance rather than look at the very obvious foreshadowing and buildup infront of them that Zoro will be the one to carry it out. It's just bias against Zoro and denial at this point.