If I were to create a plot for the world of cars, to MAYBE work between cars 2 or 3, but specifically right after 2, like a cleanup of the consequences of what the lemons did, with the zundapp leading and maybe manipulating the heartless, but what happened to clayton happening, and about how the keyblade would work, I imagined it could be like the weapons on the metal part of the car's wheel, it would simply be glued there, and the combat would be mainly with projectiles
But I really think that an entire world of cars would be kind of absurd, and I believe that the controls in that world would be a disaster of stability like atlandida in kh1 (I imagined having a camera further away from the character and drifting while shooting magic at an enemy)