Eh, with lane keeping features I don’t think it’d be hard to at least detect someone swerving a lot. Granted, I don’t think that would detect people that aren’t super drunk, but it’s something.

I might be wrong on that assumption - I don’t drink, myself.

As is commonly commented on by cartoonists: In plenty of places driving consistently within the lines might be the actual sign you're drunk. Because the roads/potholes are bad enough that you shouldn't be, if you value your suspension.