Problem with that is that it implies that you are the one purchasing the features for that vehicle. If the vehicle is sold as used then you unlink the VIN from your account so that the new buyer can register the VIN to them. Then the new buyer seems to have “nothing” and has to “purchase any of those features permanently” again.
With such a system in place, I could imagine that a proper Audi dealership can be authorized to “continue a permanent subscription” to a new used car buyer (or Audi can just offer those sorts of upcharges at the point of sale).
Regardless, permanent only likely applies to your ownership and not to the vehicle itself.
Looking around a bit, it seems like you have a myAudi app which you register your VIN to which then lets you access the additional features.
https://www.audiusa.com/us/web/en/about-myaudi/vehicle-functions.html
Problem with that is that it implies that you are the one purchasing the features for that vehicle. If the vehicle is sold as used then you unlink the VIN from your account so that the new buyer can register the VIN to them. Then the new buyer seems to have “nothing” and has to “purchase any of those features permanently” again.
With such a system in place, I could imagine that a proper Audi dealership can be authorized to “continue a permanent subscription” to a new used car buyer (or Audi can just offer those sorts of upcharges at the point of sale).
Regardless, permanent only likely applies to your ownership and not to the vehicle itself.