In the news over the last couple of years, I've seen more than one report of schoolchildren stopping a runaway school bus (driver passed out, etc.) by turning off the ignition key. So this behavior can be a feature, not a bug.
Turning off the engine doesn't have to be attached to the mechanical ignition switch.
There are already cars where the ignition switch is completely wireless and software-controlled. For example, many cars offer a start-stop feature which turns the engine off when standing in red lights and automatically starting it again the foot moves from brake pedal to the accelerator. People are going to learn that there's no such thing as ignition switch anymore.
Motorcycles have red kill switches that shut down the engine completely. A school bus or a car could have something like that.
