Audi has that on A8, or they had, not sure if it's an option on the latest generation.It's been done, it's just useless. All the Prius one has the power to do is run an electric fan for car ventilation when parked: (no A/C tho)
To be honest, I don't see why it's useless - Audi also used it for cooling while parked and A/C is off. The situations where it helps, parked car in the Sun in summer, is exactly when you'd have lots of sunshine. And having your car be 0-10C over ambient temp instead of 30-40C when you come back doesn't sound any less useful than say heated seats in the winter.
I'm thinking it's more about the price and perhaps extra weight than being useless.

