This is an interesting idea, same with coinhive.
We've considered making a plugin that allows you to opt-in to a web-based mining pool so that you can get rewarded while you browse the forum. Mining in the browser is a bit expensive though, so maybe on the lowest setting with enough people in the pool would something like this be viable. The result could be something along the lines of each user getting a very small amount of crypto very often.
On the lowest setting for coinhive (1 thread):