I think once you get down to the size of vehicles like this: www.youtube.com/watch?v=R2oD1ZHNMFE then they become naturally modular/replaceable. At least in the same way that bikes are. I don’t think people really create “modular” bikes they are just naturally swappable. Of course standards are helpful, and I think there is a total lack of standards for golfcart sized enclosed vehicles.