For a true proposal, we have to make it in a few languages. Hereby a list of ideas, later to be transformed into a proposal. Please feel free to edit it.
We now have a free encyclopedia. We now have a free library. We now have free pictures. Now we have to free the music  and make it available for everyone. But with the preservation of the wiki-idea: publishing music with a free license, or publishing music in the Public Domain.
Let's make a WikiMusic. A Wiki with:
- both score and text of a free piece of music
- the music itself in a playable music file (in different versions, for example one version with trumpet, one with a whole orchestra, not MIDI)
- the sheet music in a wiki-text format
- information about the piece of music.
The WikiMusic has to be user-friendly as well. So NO WikiMusic just for expert musicians, but also for people who are just looking for a nice work of Beethoven. There has to be a system to search in this Wiki in a user-friendly way, too. Maybe the so-called Parsons code can be used?
The WikiMusic wiki has to allow for growth. Not just for experts, but rather also for people with little knowledge of the software. Lilypond is at the moment still too difficult, too technical, for this purpose. Maybe there are possibilities to make it easier to enter scores into a Wiki. Maybe it is possible to integrate some kind of keyboard (java applet) in the software, and have the software rewrite it into Lilypond-like formats. Perhaps a (java) applet to drag and drop the notes into the score can be developed, so a full score can be reproduced in a Wiki. And that such will be transcribed into the Lilypond format automatically is our dream.
The Wikimusic has to be editable. So not just the creation of new scores has to be easy, but also their editing. Maybe some way can be found to change the rather complex format of lilypond into a drag-and-drop idea, so the sheet can be altered easily. Later the sheet can be transcribed into the standard format again.
WikiMusic must, last but not least, be able to survive. Not only with its envisioned community, but also with a protection from vandals. It may prove to be be hard to maintain the usual wiki-way here. Some brainstorming about this issue needs to be done. How can vandals be checked best, by a mere possibility of listening to the differences perhaps?