"I really like the idea of torrents being used to distribute anonymous derivative works of copyrighted media."

This reminds me of fan-provided (third party) commentary tracks.

Are those still a thing ? When I first heard of this, many years ago, I was very excited about the idea of seeing interesting films with interesting background/commentary/metadata provided by well-informed commentators.

Did that ever go anywhere ? Do people still do that ? Any golden examples of this kind of work that I should look into ?