I don't have all the details worked out, but heres basically what I was thinking:
An option that allows to to choose different music that you hear in Haven! You just pick a song, and it will be saved so whenever you go to Haven, you'll hear that music. To benefit OOO, I was thinking you'd have to buy individual songs.
Example: On the Hunt (20 CE) etc., etc.
http://souleatercomdeyclub.deviantart.com/gallery/29327495#/d3ad6ea