I think that's clever. So you keep one song or key ? Pay for the key then you own the song so you charge as you wish ?
The charges will be in Opus coins ?
Opus token (OPT) is used by listener to purchase decryption keys (songs) and the price is made by the artist itself. The tokens also can be used by artist to promote their songs indirectly through the artist bounty. Feel free to read FAQ here :
http://opus-foundation.org/faq.html