We already have a system in place for this: civil liability and criminal culpability. If you hack your car negligently, you can be sued for negligence or charged with manslaughter.
Neither agreeing nor disagreeing with you, but it follows that you should also maintain this: "It should not be illegal to drink alcohol while you drive. If it affects your driving performance negatively, that, in isolation, is what should be penalized."
And because the impact is exponentially larger. Arguments for regulation prohibiting individuals from tinkering with their cars does no such thing, because those laws are not currently in place, and there is not an epidemic of runaway user-modified vehicles.
On the other hand, such regulation would serve to prevent users from enjoying the property they purchased and to facilitate exploitative practices by manufacturers and retailers. It is all the more absurd given that existing law already provides mechanisms for deterrence and punishment, namely: the notion of negligence.
I cannot stress how terrible this idea is. This would severely degrade consumer rights and do virtually nothing to protect people.
It really depends what you are modifying. By all means have a custom entertainment system and I detest the software locked features such as heated seats.
If you are messing with safety critical software then it is no help to me that you are prosecuted for negligence if I am killed.
Even if your safety critical software works it still is negligent, there should be some barrier to entry for such software. It shouldn't be out there in the wild made by whoever with no oversight.
