I don't see that sort of thing working. Too much relevant gray area. For one thing, something that is playing in the background, where it doesn't sound good as

I don't see that sort of thing working. Too much relevant gray area. For one thing, something that is playing in the background, where it doesn't sound good as music and where there is talking over it, isn't the same as having music edited in with good quality. Using 10 seconds of a song, in high quality, for your opening title sequence is probably a lot more of an infringement than having 30 seconds of dialog, where there happened to be music from someone's car radio faintly audible in the background. I'm not arguing for the status quo (I think it is very broken), but I don't think such simplistic solutions would actually work.