Here's a plan:
Combine Spotify playlists,
Blaine (federated content),
OAuth,
last.fm Boffin/fingerprinting,
listen.grooveshark.com,
and Simplify Media
to make an index (distributed?) of everyone's music libraries,
searchable and accessible only by approved contacts,
and playable from anywhere.
With opt-in for royalty payments to copyright owners for public performances, where access is unrestricted?