Hmmm, I do like the idea of crafting or finding music. I know Minecraft lets you craft music records to play in the jukebox. However it makes more sense to find something. Perhaps whenever dungeons are added, that can be one of the treasures to be found, to unlock new music. Heck, a piano roll that could be fed into one of those auto-playing pianos would be pretty neat too
My only complaint about the music currently is there's one particular piece which has the sound of howling wind in it. When I first heard it, I thought it was hauntingly beautiful. I was in the winter biome at the time and combined with the sound effects ( which like you said in your link, the sounds of walking on snow and snapping twigs all add to the realizm) sounded appropriate for that setting. However I've heard the same piece in other biomes as well where the weather seemed calmer. I hope that eventually the sound effect will be removed or if the music would only be played during eerie weather such as strong winds, rain downpour, and blizzards. I feel that the sounds and music are detailed and organic and given the amount of detail Red is putting into this game, it should be an experience as well as a game when its all done. The sound pieces are there (there are TONS of sound effects packaged in the game but not all of which are implemented yet), just needs some more arrangement.