In reading the article, it says it samples the air in the cabin. Yes, the sampling device is placed on the steering wheel, but what if you are a DD for 3 or 4 very intoxicated people. Would this device be able to know that the alcohol in the air did not come from the driver, not a chance.
If you want to implement something like this, can't you do it like they do with Diabetes testers?!? The ones I have seen take only a few seconds to give you a reading, with a small sample of blood, can't you just do they same here, instead of reading blood sugar level, read alcohol level? It may not be 100% accurate, but it should do the trick. If you are close enough to the legal limit that the meter says you are over, you probably shouldn't be driving anyway.