I think you are right, I hope they don't push it in a half assed state.
Achieving the accuracy is not the major problem here, but keeping it accurate. You have to make it robust enough so it doesn't fail at random (sensors in general are a bitch in this regard) and it has to hold a perfect calibration for long enough (a assume chemical detection sensor, which again, are a super-bitch regarding calibrations), while also making it at least a bit hard to bypass. The other problem is the privacy nightmare this can be, analyzing fluids or cameras pointing to your face... are they gonna sell this data to insurance companies (just as an example, it could be other companies, your employer..)? Of course they are!
The only thing I would expect from this is a lot of people pissed or worst because of malfunctions while all the drunktards stay on the road by simply filling a ballon before they start drinking.
Mother Against Drunk Driving (MADD)
Aaaand of course this is been pushed by some Puritan-Americans lol