In current state, when you hit RR80, there is no development for your character, even at RR 100 or more (and nobody achieved that yet).
Idea 1: You will continue to gain renown point with every new renown rank, even past RR80.
Idea 2: At RR 80, 90, 100,..., you will get one mastery point to spend.
Renown Ranks above 80 takes millions of renown, and the progression is slowing down dramatically, so this it not an OP solution, and it will keep players fighting in truly never-ending war.

THX for reading.