I love YouTube as a grey-area on-demand radio.. For a really simple music mash up I also made http://fmix.heroku.com .. Enter an artist or Song you like, click search for a last fm generated then randomized list.. Jump from a song you like into a new list.
Has its limitations but works quite well for bgm (except when YouTube search gives a false positive though this can be hilarious)
Interesting idea, get many people to edit the same JSON file.
I'd imagine you'd need to do a lot of hand merges, because everyone will try edit the same files section though (notably the bottom of the list), which in part ruins the whole "everything is a PR" vibe. Shame, because the idea of talking over changes in the comments and then pulling it in is cool.
So the idea is that people fork the project, send pull request and then get them approved to add songs? I am pretty sure that we have the whole html form to database dance figured out already...
Has its limitations but works quite well for bgm (except when YouTube search gives a false positive though this can be hilarious)