Foldcoin is very similar to what you're describing. The problem is that it's not actually clear we can do what you're describing in a cryptographically secure w

Foldcoin is very similar to what you're describing. The problem is that it's not actually clear we can do what you're describing in a cryptographically secure way - foldcoin for example essentially relies on the security of the Folding@Home network, something I find extremely sketch​y. Regardless, it's not actually clear that Folding@Home itself is a net positive for society anyway (see https://www.gwern.net/Charity%20is%20not%20about%20helping https://www.gwern.net/Charity%20is%20not%20about%20helping)