In-game music already exists, mayhap a portable jukebox which allows you to play and switch songs to every Entropia/PE song, both new and old would be easy to implement, and give enjoyment to some players.
Don't make it decay though that would show too much greediness imo.
I can see why it's not planned though. A simple search on google or on this forum gives link to all the old music and new from Entropia, and any music player would be able to play it.