I've always been interested in deep economy games where the economy drives the gameplay to a degree. The main reason for that is in my mind it's a really easy starting point to the question, how do you provide a space where the player can change / shape the world, while still having the world push back, return to normal or if successful, converge on a new normal?
So for example take any zacklike, one thing I'd like to try is having something like those mechanisms drove the supply of goods in an in-game economy, which would then feed in as input into other systems.
Well any complex system as the input would do =)...
So I've spent a lot of times tinkering with economic simulation games, the tricky thing is making them fun / balanced. I'm still trying to work out nice ways of debugging them when they break / become unstable. A lot of it at the moment is plotting data over time to see where failure points occur.