Music packaged as normal Add-Ons 'n stuff.
Explanation
Let's use this as an example:
Music_Default
Music_Default would include all the default music, and would be downloaded with the game.
Files:
Music_Default.zip
|-music
|-After_School_Special.ogg
|-Ambient_Deep.ogg
|-etc...
|-description.txt
|-server.cs
All of the music would be included in a "music" file in the .zip. Server.cs would do NOTHING, nothing at all, just like prints. Description.txt is just the same as with other Add-Ons.
But... Why?
3 Reasons:
1. Don't need to do that little bit of effort by saving in music file, just save in the add-ons folder.
2. So RTB won't need to do that hacky thing it did in version 2 to download music.
3. No need to download lots of music or extract a .zip or .rar file, as you can just place a lage music pack directly in the add-ons folder.