Champ Mastery 6&7 Should Require Getting S- in X out of Y Games to Show You Consistently Play Well.
This would show that we can consistently perform well on our champion when tryharding, and having that level 6 or 7 mastery will feel like a huge achievement depending on the numbers you use. It's fairly difficult to get an S- in 3 games out of 5 or 7 out of 10. That doesn't have to be the exact requirement for unlocking mastery 6 or 7, but you get the idea.
This system could work via toggling a challenge in the Hextech interface to start counting your performance in your games, sort of like a toggleable promo series but with champion mastery. The reason for the toggle is so that people can toggle it off when they just want to play casually, and no progress would be lost.
A forseeable issue with this is that people will just smurf or play in norms where there mmr is low, so champion masteries 6 and 7 should only be valid in your highest ranked tier and below (including normals).
For example, if you were successful in gaining champion mastery in gold, you would have it in all divisions of bronze-gold and normals forever (Unless the champion has a significant rework like Sion, in which case it should be reset) but not in platinum+. You should therefore be prompted to select whether you complete your champion mastery test in normals or ranked. Whether your champion mastery should be valid for the tier you started at or ended at, I am indifferent.
tl;dr: Champion Mastery 6 & 7 should instead be unlocked by earning an S- in X out of Y games (ie: 5/10, 8/10, etc.). You would toggle this system on via the hextech interface, and it could be toggled off without losing progress if you want to play casually. To combat smurfing for mastery, champion mastery would only be valid at the ranked tier you achieved it in, and all tiers below (and normal games), and you must select whether you wish to complete champion mastery in normal games or ranked games, you cannot mix both.
Oh and also we should really get the champion portraits as icons.