More than anything I am nervous about having a car running priority code that can have mandatory updates pushed at any time that change the cars behavior -- not just throttle response and adjusting the emissions here, they could be updating thresholds for when the auto-pilot cancels and return to manual control, what level of cruise the car defaults to (GM BlueCruise IMO is terrible about this, it cancels hands free mode often, without any auditory alert) and so on.
Give me a car without internet uplink any day!
That's my issue. You could drive the car one day, go to bed, and the next day the car does not perform the same way it did yesterday. That's ridiculous. Any update needs to be approved by the user. Even if that means doing like Apple does where the user has to enter their password to approve the update scheduled for the middle of the night.