Maybe if you're blind it would make it easier
I can't see it being any real help, though, well maybe if you're blind it would help a lot . We have stereo already, so (bearing in mind you have the sound of your own car in the equation too, we don't want the weird effect of the volume of your own car being turned down when there are others nearby, like I noticed in Forza)...so if you hear a sound on the left, and you can't see a car in front of you, the sound is alongside or behind you on the left. If you hear a number of sounds on the left, and only see one car, then there is probably one behind or alongside you on the left. Easy.
What I would much prefer, slightly OT, though, is no more disappearing cars when you look away from them in replays. The sound they make disappears too, and then when you look back to them they take an annoying instant to reappear. Thank god it doesn't happen whilst playing, spoils replays sometimes, though.