Food for thought: Pandora's Music Genome system is proprietary but you might be able to reverse engineer some of it based on what we know. Page 7 of this slide has some of the tags that are embedded in some of the tracks.
Pandora hires people with music theory and musicology backgrounds to tag the tracks manually (a little surprising considering how goofy some of them are) but I think that these tasks could be built into a blockchain protocol as potential rewards for keeping the tags fairly clean. It would also remove the burden of self-tagging done by musicians -- which, at least in my experience, tend to be more of a chore than anything else.
I think that music genres (Pop, Rock, Classical etc.) should probably be broken down in a generic and neutral way for ease of maintenance -- and possibly even restricting each track to one per genre at first to reduce the noise and confusion that exists right now. Best not get involved in categorization battles here. But tagging should be done in a decentralized way, imo.