What, for example, if you're living in a rural area, then your wife goes into labor (or there is any kind of other emergency) and the car thinks your somewhat "erratic" driving style, due to the stress of the situation, warrants killing the engine? It only talks about detecting "impairment" which may mean a lot of things. Or maybe you had a beer and then the emergency happens, and the car detects "passively and accurately" your BAC.
Banning drunk, drugged and impaired driving is good. But every rule has exceptions, and software is generally too rigid to account for every possible exceptional case.
There won't be a "It's an emergency" button (because a lot of drunks would just press it), nor a "I am lawfully driving on my own private property" or a "I am not actually impaired, I had to drive 'erratic' a moment ago not because I am drunk or fell asleep, but because a kid ran into a street and I had to do an evasive maneuver" one.
That is assuming the software is working "correctly" in the first place. Which I am very doubtful about here, because they aren't trying to model something deterministic, but model something that will use some kind of "learning" to spit out some probabilities.
That aside, the privacy implications look pretty real to me. Once you have a system that monitors your driving proficiency, BAC or both, a lot of companies will get curious about that. Insurers may start to politely ask for the data if you want lower premiums, or a contract at all. No more car leases unless you can provide a "positive" driving score. Judges will sign warrants for such data. And so on.