I think the big blocker for an offline, subscription free Spotify-like experience is lack of a central repository where listening data from all users is stored.

I think the big blocker for an offline, subscription free Spotify-like experience is lack of a central repository where listening data from all users is stored. You could do some things with metadata on the songs themselves but automated playlists like Spotify and Apple Music have to my knowledge rely on models trained with vast amounts of listener data. You could patch something together using last.fm as the data source maybe, but I don’t think scrobbling to last.fm has been popular for many years at this point, which is going to severely limit the quality of generated playlists for newer music. Additionally, last I knew last.fm’s API was still XML based which makes it not so ergonomic to use in today’s JSON centric world.