I think the solution to MUSE_USD lies in its use.
How will users pay for MUSE? Can they use PayPal or credit card to purchase MUSE (formerly NOTES) via PeerTracks? If so wouldn't PayPal_USD ≈ CORE_USD? In my mind MUSE_USD would simply act as a basket of currencies denominated in "_USD" throughout the ecosystem.
People wishing to buy music, merch, concert tickets, tip, patron, etc. whether doing it on PeerTracks or any other website that connects to MUSE can do so using Smartcoins/MPA.
In this way, both consumers and creators (artists) do business in a currency they are used to (the USD for example)
No need to understand crypto currency, blockchain or any of that "nonesense"
Products are denominated in familiar ways (as opposed to paying 0.00017BTC for a song download) and of course they are shielded from volatility associated with crypto or stock markets.
So the muse_USD will be currency of the music industry... Collateralized by the MUSE core units.
Make sense?