I don’t know if that would be the best idea, since most people just watch the beginning of the video. If you had an intro with a song, than the people who claimed the video would get most of the money off of the video as a whole...
What if you used multiple songs in one video? What would happen then? (Like if you made a video with 50% music? YouTube already takes ~45% of ad revenue, and now there are people getting demonetized left and right. I don’t think the community would be happy...)