How About Rank 8?

Rank 7 is just easy to get if you dedicate yourself to a champion. You have 3 good games then you blow 4300 IP to get blue essence from champ shards.

Can we move onto something that is actually challenging and denotes a player's actual skill with their champion?

I'm talking a possible Rank 8 Mastery.

And to earn it, players would have to receive 4 S+ scores on the champion. Unlike other Mastery Tokens, however, these could decay over a period of time unless used. Each one could disappear from your inventory in say, 2-4 weeks after earning it, for example.

So to become an actual master of a champion you would have to play that champion exceedingly well within a set time frame.

To compensate, I'd say eliminate the blue essence required to unlock this particular mastery. It'd simply be a true test of skill.