Dare I say it...?
ZKK or Zoro defeating Kaidou is coming.
Oda is slick, he's going to leave us with a humongous cliffhanger before the month break for certain. Law and Kid are about to set sail. If Big Mom and Kaidou return, Luffy and Zoro are the only ones close enough to stop them from destroying Wano Capital.
It will all start with Orochi Castle being burned down, then those monsters will emerge.
Luffy will fight Big Mom and Zoro will fight Kaidou. Why? Duality and parallelism. When Zoro and Luffy first fought each other they also had to sidestep Mr. 5 (a
bomb man) and Miss Valentine (their devil fruit ability mimics how Kaidou was defeated using gravity). Zoro and Luffy both easily overcame the things that ultimately caused Kaidou and Big Mom's downfall.
Zoro and Luffy are being painted as equals for a reason. Even now they're mirroring the behavior of Kaidou and Big Mom. They're even hinting that Sword God was on the same level as Joy Boy.
This parallelism even fits perfectly for what happened after Zoro and Luffy fought, and for what will probably be the next arc's focus.
Saving Vivi.