After a discussion involving Markus of the unofficial Edain Discord server, Oakenshield224, Necro and I, I'd want to make a suggestion regarding Might of the Witch-King (and sort of expanding on Necro's suggestion of Ring Hero WK and that power).
The Might of the Witch-King power is defined as a counterpart to the Gifts of Lórien ability of Galadriel, giving temporary buffs to a particular Angmar hero, whereas the Galadriel version gives permanent buffs. To help equate both abilities in usefulness, I think this could be done to improve Might of the Witch-King (considered underwhelming by some):
At level 5, WK would get the ability with the temporary buffs, plus, the ability would grant a cooldown reduce to the abilities of the hero who has gotten the Witch-King's favor. This was an idea by Oakenshield224 that would allow to get a better buff for the heroes affected by the Witch-King's power, and not to be too OP for a level 5 ability.
Meanwhile, at level 10, the ability would be improve to actually have the effect of reseting ability cooldowns. This would keep the theme of WK's abilities being improved at level 10 (like Death Blade and Life-Drinking Blade). The reset effect would only be at level 10 to avoid making it too OP in the early game.
It would be comparable to Prince Aranarth's level 10 ability, which includes a buff apart from a cooldown reset for every nearby hero, while this power would be only for a hero, setting it apart from Aranarth, but the additional and original effect would help setting it apart from Elrond's level 7 too, warranting the level 10 unlock for this improvement over the power.
As an aside, and building of Necro's suggestion to make Ring Hero WK's Might of the Witch King effect all nearby heroes, I believe the cooldown reset could have this change aswell when the Lord of the Nazgûl gets the One Ring.
I hope you like this suggestion, feel free to express your thoughts!