The basic sketch is to have a way to feed back information about pricings into the block chain. There are then a few ways to increase/reduce the currency in circulation, some of which involve creating coins and some of which involve shifting incentives for holding coins. Most of what remains, then, is a control theory problem.

My current issue is deciding what should actually be targeted. Targeting a single currency or commodity has most (though not all) of the downsides of just using that currency or commodity more directly. Baskets of goods is one approach. Other statistics are also good candidates, though - stabilizing the mean rate of change across a lot of goods, or the like.