My prediction-

This emp-like shutdown won't work very well for a long list of technical reasons. (engineering judgement on my part)

But the sales job will cause the LEO community to demand the ability to halt high-speed chases and carloads of terrorists.

The feds, responding to LEO demands, will require that all vehicles have embedded within their onboard computers the capability of receiving, processing, and executing commands (like "shut down" or "brakes on now" or "continuously honk the horn so we know where you went")from LEO transmitters.
This is a simpler, more effective though totalitarian solution.
And if bystander vehicles are shutdown.... big deal. They can be reset. (unless there is a crash resulting but hey, that's the price of freedom from high speed chases)

I predict it will happen within 10 years. Perhaps as early as 5.

Next year if Osama is spotted in downtown LA and the LAPD is unable to catch him and the chase is seen on TV....