"Safer", sure. It's safer still to keep seperate systems and avoid monocultures.

Cutting engines is already possible. The devices used by police in "2 Fast 2 Furious" are a bit fanciful, but actually not far from the truth. There are systems that can cut any engine by bombarding the computer with microwaves. This uses a fundamental vulnerability in semi-conductor technology.

There are also lasers microphones which can pick up minute vibrations on a window, thus letting you hear whatever is inside. IIRC, it was recently ruled in the US that police need a court order to use such a device.

In either case, the technology is available to do these things now, without exploiting the car's OS.