I want my car infotainment system to run Android, so that I can use my favourite car-adapted apps to run the radio, show me the map, play movies, whatever Android can do. (Change music depending on where I am? Why not. Use voice commands? Why not. Future application I didn't think of? Why not, it's Android.)
Then whoever feels like running interfaces like this, can do that, just download the app.
But then the car stereo shouldn't be on a more important CAN bus that it can possibly control the AAC, far from any driving control or unlocking of the car.