Sure, it’d be possible if the attacker had physical access to the car long enough to install new hardware. But if you’ve got that, then there are already plenty of ways available to you to kill the dude. If you want to keep it simple, just put explosives in the car, timed to go off while they’re on their accustomed commute. Or, heck, if you can get into their garage, you can probably get into their house, too. Smother them in their sleep with a pillow.
2003 Mercedes E-class had a system devolved from the earlier S-class that was essential electronic/by-wire braking. The backup was a physical linkage that came into play if you pressed hard enough.
As the '03 E-class was extremely beautiful and had no fewer than three undercooked controllers that controlled absolutely everything in the car, and required reprogramming once a week, I’m just as glad we got rid of it. It got ridiculous to have to go in for reprogramming because the exterior lights wouldn’t come on (or go off), and the sound system randomized channel selection, and the engine quit, and… let’s not talk about the brakes. OTOH, I got to drive some damned cool loaners, including a couple of AMGs.
Way back on 07/09/2013 in Post #23 above, I prophesized this:
Fast forward to mixdenny recent Post Office Conspiracy thread where, on 12/18/2019 I wrote:
Did I call it right? WELL, DID I? Your car is watching you. And Big Brother is watching you, or will be any time now. Your always-on-line autonomous car will decide when you go and when you stop and where.
And yes, car control systems are being hacked through the on-board entertainment system, which is apparently is not all that isolated from the control system. This isn’t even all that recent: Hackers can now hitch a ride on car computers, Jerry Hirsch, Los Angeles Times, Sep. 13, 2015.