Finishers as Champion Mastery rewards?

I just had the idea to use new versions of the kill finishers from urf as rewards for the top teirs of champion mastery. It could be a good reward that has no monetary or game-play impact, it would only appear on the champion(s) you have at those teirs and could be as simple or complex (probably simple) as riot deems. Maybe something as simple as the mastery icon appearing above their copse (marking your kills) or just a shiny light explosion or something.