Well done! I like your design approach: artists as seeds in a controlled genre-based expanding similarity selection. It is like a recommendation system but limited to your own music library content.

Just a simple suggestion: allow for copying the result as a text list (I'm one of those who can tolerate you reading my data but not writing in it)

Some of you may be looking for more "plain" ways of recycling your library (where you more explicitly choose the final outcome) by

- (re)organizing (by genres, popularity, date added, audio features...) -> http://organizeyourmusic.playlistmachinery.com/

- (re)combining (using a good selection of modular dataflow operators) -> http://smarterplaylists.playlistmachinery.com/

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Bonus : https://observablehq.com/@mjbo/genre-map-explorer-for-spotif...