I've always thought that music recommendation systems should look at the actual music, and not as much at the surrounding meta-data.

What kind of instruments are used? What key is it in? What structure is the song in? i.e does it have a standard format, is it prog, is it a symphony etc What language is it in? What Rhythms are used?

That information, used properly, should be able to actually recommend music that the listener enjoys, not just guesswork that is usually rubbish. The Spotify algorithm for example...