I actually was talking with my engineer about such a system and the feasibility of developing it for the AC Market.... sort of a reverse Portable People Meter set up at strategic locations in Atlantic and Cape May Counties. The problem, I was told is that it would be too difficult to pick up the signals from each car radio.
That technology was developed, deployed and, most important, patented. Hundreds of sensors were mounted on poles along freeways in LA and Phoenix as well as on surface streets, and the system picked up the radiations from passing cars. The whole thing worked, and quite well.
It was not difficult at all to pick up the signals.
Advertisers and agencies did not like it, as it only covered in-car, and had no demographic information; it was as useless for buying as it was for selling.
There must be a better and cheaper way to establish ratings.
Advertisers don't want cheaper ratings, they want better ratings. That is why radio was more or less forced to pay 60% more than in the past to go to the PPM in the top 50 markets.
As a former software engineer/scientific computer programmer for the military, I dealt with far greater challenges. This doesn't seem all too difficult but rather the real problem in my opinion would be in gaining acceptability and the cost involved.
As I said, if Nielsen tried and pulled out of radio, despite their decades of experience and deep pockets, it is really unlikely that any one person can come up with a solution.