Chests for Mastery

When the hextech system was implemented it also added mastery 6 and 7 to encourage you to main your champions to get higher than mastery 5 on them. If you are rewarded for playing a new champion and getting a chest I believe that you should also be rewarded for playing a champion for a long time and getting 5 s ranks with them with a chest. I mean its not hard to get s ranks so you should be rewarded for playing a champion for an extended period of time.