Since it lacks a Mythic+ difficulty, what if we got a wave survival type instance set in Violet Hold? It could award gear based off waves survived, with break periods every 5 or 10 waves. It could even have a keystone-type system where you can choose to save your instance at a break period and come back later to the same wave you left off at. This would, of course, be separate from actual keystones. Could have boss waves and even waves with multiple bosses.