I'm even thinking (outside the box here) that one could say "This is worth 1 USD, and is to be used only for purposes of transferring value between accounts". Rules-based system where everyone participating in that particular ecosystem is participating based on the rules set forth by the coin. It's obviously not supply / demand, but since technically it's never used for anything but transfer of value, you're simply creating a mechanism by which people can avoid transaction fees (ie. PayPal, and name your current cc processor).