The ability to slot active abilities as passive would be fun.
You would have a primary and secondary bar, attached to your weapon slots like the active bars.
Abilities slotted here would normally have reduced but constant effects, and reduce max resources or resource generation.
Ultimate would reduce Ultimate regeneration and normally have greatly weaker effects than their active counterparts.
Most abilities would become passive effects or auras.
Some might have an auto cast feature.
Some might have proc conditions.
Beware, because they reduce your maximums, you will have reduced damage if your damage is from the reduced resource.
Choose your skills wisely.
I'm still in the process of designing a theoretical function for each ability, mostly being pulled from ESO Hub.
I've got most of nightblade, weapons and armor and a few guilds.
I would use this, but I also foresee some people hating it because they lost 30 damage when trying it out.
I still think it will be fun.