Start out by being a physical gold clearing house. When you issue currency, you have the gold in stock. Each currency bill has a crypto address printed on it, and the bill is made to be counterfeit resistant in other ways, possibly by having two crypto addresses on it, while being listed on only one of, say, twenty revolving blockchains. The hash of the two addresses determines which blockchain it is on, so that the user can safely see that his is not a counterfeit piece. --- Well, there's a little start. Anybody want to fill in the rest of the details?