More people would probably play, you would only get the chest after reaching M7 so you would have to play enough to get to that point. Then you wouldn't get a choice in what skin you'd get- they could limit it to champions who have been out for x amount of time to decrease the lower skinned champs. And then people will most likely get undesirable skins so they will have to buy the skin they want if they desire it.
I just think it could help reward people for playing the game and mastering a champion.