Luffy's big payoff in my mind will be opening Wano's borders in some literal fashion. In every major arc, Luffy has followed up his objectives through action.
He wanted to beat Crocodile, but also Alabasta needed to learn the truth of his, Crocodile's schemes, and Luffy not only beat him, he punched him outside the hidden catacombs/his lies out onto the surface for all to see.
He wanted to prove Sky Island existed for Crocus and Noland, and he rang the bell of Shandora which proved it, while simultaneously defeating Enel.
Now, I think he'll defeat Kaido in a way where the literal obstacles separating Wano from the rest of the world will be removed, or Kaido goes through with his New Onigashima project in develops literal borders around the country so Luffy can beat him while smashing them all. That doesn't seem too likely as of now, but it's something to think about.
All and all, I believe Luffy will defeat Kaido while symbolically and literally opening Wano's borders.