I don't know how this would even make sense, but Kaidou and Big Mom will somehow survive being bathed in magma for months, until Wano's borders are finally opened.
Zoro would then slay the dragon above Wano's true capital. All those little ZKK hints Oda left in the covers and Color Spreads will all be redirected to using chapter number clues in future chapters. Wano arc's only purpose was to lay the ground work for ZKK. Even Luffy's Gear 5 Sun God form was to set up Zoro's surprise Sword God form.
History is what Oda wants to repeat. Oden's Legendary Hour will come again. Yamato is already dead set on the path to repeating Oden's life story. Oda is clearly saving ZKK for the second half of the Final Saga. This was always the plan since the very start. My theory is Luffy and Zoro's ancestors were mortal enemies, but now their roles are reversed. Luffy and Zoro are like Yin and Yang. Zoro is the secret antagonist. Perhaps the reason why we haven't seen another Time Fruit was because Toki herself was the Devil Fruit. I think the Void Age was to cover up the Ancient Oni race being turned into Devil Fruits. Toki was an Ancient Oni, but she also brought Zoro's parents with her as well. Zoro's parents got lost trying to go to the original Shimotsuki Village in Wano, but instead wound up in East Blue's Shimotsuki Village. Zoro is the son of an Ancient Oni and a samurai who participated in killing the Ancient Oni race. This makes Zoro a half devil fruit with powers of Asura, the power to manifest his spirit. This makes Perona and Zoro's pairing during the time skip a ghost and spirit combo. This will result in Zoro creating his own crew with Kaidou as a crew mate. Luffy vs. Zoro Civil War.