>Coming up with a way to have a decentralised currency where everyone involved gets a fair say without consuming too many resources is a super interesting problem.

I think the obvious solution is to do useful work rather than throwing away work on crypto. Have miners solve real problems and give them credit for getting the right answer.

This is what Ethereum is supposed to do. I don't think it's a great solution. It's still extremely wasteful since every node runs every computation. Even something like TrueBit, which is designed to be scalable and efficient, is still far less efficient than normal cloud architectures. It still throws away the vast majority of the work in the interest of safety and incentives. These systems are good if you want trustworthy computation, but not if you want high-performance and power-efficient computation.

I'm trying to design a system where something like 95% of the work goes to useful computation, but I have nothing anywhere near shippable. It's a hard problem.