Maybe one vehicle at a time can be hacked, but shutting down a large number of vehicles at once is too massive of a project even for a large hacking organization based just on the GPS logistics and the necessary ground infrastructure alone. Sure it's real now but on a minor scale, and only for a brief little window in time. Fossil fuel cars are on the way out, and with them the kind of computer engine controls mandated by anti-pollution laws and fuel mileage laws. GPS won't be linked to engine controls at all on electric cars. No need to. Won't need remote starting.
TC