I like the idea, there are some issues that you'd need to work out (it would be extremely easy to cheat and with money involved you need to find a way around that).

But you might want to read up on your understanding of 'proof-of-something'.
For example steem works on proof-of-work just as bitcoin (or ethereum for that matter) does so you have just as much waste of energy. The difference is that bitcoin gives all newly minted coins to the miner that got the 'proof' first whereas steem gives (a part) to the content creators but that has nothing to do with the proof at all. Admittedly it's quite complex and not that easy but might be worth reading up on it :)