This bothers me in a bunch of ways.
First, is implementation.
I can think of two ways of doing this. First is local radio, or light based communications. All automated cars broadcast, and then a reciever determines who's where, so the officer can direct a specific machine to stop. Then that box has to transmit the right code to casue a car to stop. I can not see how that protocol will not be hacked and abused in weeks, if not hours of implementation. That's it's own little version of hades. If "anyone" can stop your car, you won't let ANYONE stop your car.
The second method, is with a database. Each automated car, sends it's location to a central database at all times. When a police officer wants to pull you over, he can scan the database and find your car, and tell it to do something. This method seems like it would be reliable. But then we have the database problem.
That database could be stolen. Now someone can track you, and knowing databases, now knows where your car has been for X number of days, weeks, or months.
Second, the police now know where you are at all times. Well, that's someone, but it's supposed to be someone safe. Third, now there's a database to sell, and a command that can be issued that stops your car. The slope gets VERY steep here... so lets tread carefully.
Lets say you have 50 parking tickets. The private agency in Chicago that covers parking tickets wants to boot your car. They pay the Chicago PD to have access to that database, and issue the signal to boot your car. ... anywhere. Lets say you're in ohio when they do their processing run, well you could be stuck there.
The same goes for registration. Lets say the state sees your registration expire, they'll tell your car that it can't drive legally. So it wont' drive. Sounds fine, until you look at the realities of where you can drive an unregistered car. Or transport it. GPS isn't accurate enough, property lines aren't drwan well enough, and many other factors would lead to disabled cars in legal places.
Finally, what if your car gets registered wrong? Someone else's car is the target of disablement, and instead your car gets disabled.
Sure, all of these things could probally be addressed with lots of time and paperwork, but nobody is going to pay me back or my time spent fixing their errors.