For any old school vanilla/tbc players, im sure the title of this thread caused more cringe than curiosity, but hear me out.
Firstly, i'm not suggesting some kind of mechanic that requires a person to have impecable timing subject to their latency. The way (most) seem to play ascension when incorporating a seal into their build is to pick 1 and build around it. This is fine and has good results, but I think an RE which encourages changing seals based on a circumstance or proc could make for an interesting play style.
Seal Twister [Legendary RE]
Your Seal of Command spreads your target's Holy Vengeance effect . Holy Vengeance lasts twice as long but can no longer be refreshed.
(essentially, you get to 5 stacks of HV then switch to SoC and spread HV to everything SoC cleaves. As HV cannot be refreshed, you switch back to SoV after 30 seconds and build 5 stacks again, rinse repeat)
Seal Focus [Legendary RE]
Holy Vengeance now increases holy damage taken by the target by 3% per stack. Holy Vengeance cannot be refreshed and Seal of Vengeance no longer causes holy damage at max stacks
(This would allow for similar seal changes on single target for bosses and PvP, creating an ebb-and-flow of burst windows)