It would be cool if after an arbitrary goal is reached (eg. Clear raid completely 6 times) you get a weekly item that let's you turn one old raid into current difficulty to break up the rinse and repeat cycles.

Just a thought i had about keeping raiding fresh / exciting for people clocking the content fast.

I enjoy timewalking weeks to go back and do an old raid, but outside of those weeks the game loses its appeal on 'off nights'.