So, I have no idea how to actually do this, but what if someone created a Bitcoin-like cryptocurrency that tied the mining difficulty to its value? Meaning coins get easier to mine when the value increases over some target value, and harder to mine the more the coin's value is under target value? This would have the effect of making the value of the currency trend towards a pre-determined rate of change over time. The hard part would be measuring the real value of the currency in a decentralized way, apart from any other currency value. That's what I can't figure out how to do.

Edit: if we can do this, the currency would be resistant to large fluctuations in price by design. It's like a built in self-correcting system because the supply will change to match the increasing demand.