We were talking in #joiito about wanting to play music for each other, but not being able to just post urls to our mp3's for fear of vexatious prosecution.
So here's my initial straw man suggestion for how to do this.
1. create a new playist format that refers to songs by a canonical naming scheme - MusicBrainz has a good starting point. These get put in URI's that look something like:
How does one resolve this URI?
Implement an app that tries several alternatives:
1. Is it in the local music collection?
2. Is it available on a label or artist website/bittorrent?
3. Is a promotional extract up on Amazon or iTunes store?
4. allow further plugins
In each case the name/title are used for an initial match, and the sing identification process defined by MusicBrainz used to be sure we have a real match.