This feels very similar to how the total work expended by the Bitcoin network can be approximated (not the current hashrate, but the sum of all hashes over time

This feels very similar to how the total work expended by the Bitcoin network can be approximated (not the current hashrate, but the sum of all hashes over time). Basically, you can take all of the block hashes, and find the lowest one of the lot. From that number, you can estimate the total work performed by the network in aggregate. The concept is basically the same here.