interesting idea but who decides what qualifies for a particular rating? would the rating be for the road in general or specific stretches?
I am imagining this is technology based such as radar, laser, accelerometer, etc and other stuff I have no idea about. The more and severe the imperfections in the road the lower the rating. The technology exists but not implemented yet fully on automobiles except maybe Teslas. Imagine thousands of cars that travel the roads daily just like how Google gathers information on live traffic time but instead it gathers information on the quality of the road. Now imagine instead of turning on your live traffic you can switch to see how rough the road is, maybe shade the road kind of like the weather radar shades the storms. That would tell you everything about the road even if it's just a stretch a few hundred feet long assuming you zoom in on the map.
I'm not always concerned about how rough road is except when I am towing. A bad road really magnifies the imperfections in the road and that's when I would find it really handy.
Dan