I think it's an untenable idea. Gadgets are limited in what they can do, and this one would not have the desired effect of significantly reducing alcohol related accidents.
In any event, it should be an option and not a required part of every car sold. It may help those who don't want to drink and drive, or who need to know if they are too impared to drive (kinda like a HAL 5000 computer in the car, i.e. it could drive you where you needed to go if need be, while you play AH on the drive over.) Otherwise imo this idea won't stop drunk driving or even reduce it effectively.
Les