I was thinking about this on the way home from work today....
What if we could have a feature where if we have just a few songs from a single album, it could scan other Subsonic servers for the remaining songs on that same album, then send a note or alert (or something else) to the admin of that server saying something like "Admin Gurutech is missing some music from his album XXXXXXXX. Would you like to allow him to download these songs from your server?" And then give a Yes/No prompt, and if you select Yes, then the songs can be downloaded by (in this case) me and placed in my album.
This would only be available to the "Admin" user on each server, and would not be available outside the Subsonic/Madsonic system.