Remember, decentralization often has high costs. Centralized companies and the blockchain can have symbiotic relationships. Just because something theoretically could be decentralized, doesn't necessarily mean it should. Especially for music - BitShares Music and Peertracks are trying to make a profitable company, not a one Currency to Rule Them All.
Anyways, I'm glad to hear that streaming will be offered. Personally, I would like to see a free ad supported streaming version, and a paid ad free version. Additionally, the user should have the ability to purchase a lossless high quality version. And it would really be gravy if an artist can optionally offer resample permission with the purchase of a song, or with an additional fee. That permission of course would be logged in the blockchain, and users with permission can be publicly verified. I don't think artist sample clearance has been done before this simple and elegantly, and the ease of use may actually encourage good market behavior (and garner positive press)
Add supported free version: average quality MP3 files
Paid subscription: high quality MP3 or greater
Paid individual songs: highest quality, no loss of recorded information, always available for immediate download
Paid re-usage rights
I also think BitShares music is perfect for the 'blockchain referral program', similar to what MethodX has proposed elsewhere in the forum. Artists who sign up other artists with PeerTracks get to receive a small cut of their friends fees - but this has to be done in a way that is mutually beneficial for all parties. Perhaps segregating a cut of the network fees into a bonus pool, in which referers take a cut proportional to the popularity of their referred. The bonus has to be big enough to incentive people inviting their friends, but not too big in which it creates a profits hierarchy. No MLM, just good ole fashioned refer a friend. I think you get the point for now, but if there is interest, we can extrapolate on this idea and brainstorm ways to make it work.
Anyways, we all know this has huge potential. Lets make this thing work!