Keys for S rankings

When you don't have any chests left for the month you should get key frags when every you get an S on a champion that has a chest available. I perform well on a lot of champion and play with friends so I never keep my potential chest earnings long but I never have enough key fragments, I'm sure others have his problem so I propose that you should get key fragments in lieu of chests when you have no chests available but earn an S (it wouldn't put the lock on that champ for chests of course it would just be a temporary consolation prize until you can earn an S again)