Champion Icons for Summoner Icons?

I don't know if this has been suggested already, but why not allow us to use champion icons for summoner icons?

Maybe when you unlock a champion you'd get that icon, or maybe after X number of games/wins with that champion you get their icon. Maybe for a small amount of RP even, or some combination thereof. I'm just not sure as to why I can't have as my summoner icon. I personally think it'd be awesome. Also, it would help make existing icons less common and thus more unique.

Thoughts? Info on why Riot hasn't done this yet?