Have you seen Huntercoin? It is a lot more like what you describe (thanks to @taaveti for telling me about it).

I'm very keen to see where the devs go. It's certainly an ambitious project and the whitepaper/game design document (they're kinda combined) has some amazing ideas which they need the team at Tractor, Set, GO to pull off. I'm hoping they can do it, as it has so much potential!