I'm only using lyft, but I wonder if they're not actually doing something along these lines already? I've noticed that the average rating for the drivers I'm getting has gone up recently, by a significant margin. Over the last few weeks I've only seen two drivers below a 5.0 and they were both 4.9. Also I seem to be getting rides at the airport faster than other people (though, it's hard to tell if these are uber or lyft passengers).