YAPRS - Yet Another PR Stunt
I admit that the idea is nice. Wouldn't we all have a nice beer (or two, three, four, five) at the pub and still be able to drive home safely afterwards? In the own car?! Great, just great!
But wait! There is a problem: what if the robo-driven car causes an accident while your were dreaming away on the passenger seat? What if the robo-car kills someone on the road? Who will be responsible? You? You're going to point to Google or the car manufacturer (as you were entirely drunk). Google? The car manufacturer? Both will hide behind tons of disclaimers.
So in the end - you will be solely responsible for the damage done by your robot driven car. Which makes the whole effort entirely pointless. In that case you will rather drive yourself, which you shouldn't when you're drunk. Pointless.
As I said - the idea is nice. File under "yet another Google PR stunt".