There are still a lot of other layers that need to be compromised past the cert for such an attack to even be possible. Even so, I suspect when such an attack does happen it will probably be for stealing cars. Your car would just wake up in the middle of the night and drive itself somewhere else to be cut up for parts. Less likely is any kind of safety issue since its so easy to take over control of the car.
There are still a lot of other layers that need to be compromised past the cert for such an attack to even be possible. Even so, I suspect when such an attack does happen it will probably be for stealing cars. Your car would just wake up in the middle of the night and drive itself somewhere else to be cut up for parts. Less likely is any kind of safety issue since its so easy to take over control of the car.