For V2G, its a simple feature that enables a car to participate and make money in the energy ecosystem. Govts have to standardize it for cars, just like mandating usb-c.
It has been standardized here, and we see articles about it in the papers for a few years. Yet only 2 or 3 cars on the market implement it and don't even advertise it, apparently still in trials or pushed aside for sexier features. I was under the impression it was not simple, as it requires more electronics and complexity in the car.