Are you aware of the AcousticBrainz[1] and (upcoming/in-development) ListenBrainz[2] projects? We at MetaBrainz (the organisation behind MusicBrainz and the other *Brainz projects) really hope that the combination of data MusicBrainz, AcousticBrainz, and ListenBrainz will enable powering a lot of open recommendation engines. :)

[1]: https://acousticbrainz.org/ [2]: https://listenbrainz.org/