The Jagged Crown is said to hold a portion of the power of every High King of Skyrim who has ever worn it, but it has no enchantments or special properties. The ancient nord verse that mentions it also says the king is the walking winter’s woe with a maw unleashing razor snow.
I just figured a unique enchantment that buffed ice shouts would be neat, but that also sounds a little too specific to be useful for the player. A shout cooldown reduction and buffed destruction magic damage might be easier to pull off and still be a little bit unique (fortify destruction damage being only only available in potions in vanilla). And I think that would still effect shout damage.
And making it improvable would be nice, too. And making it fulfill the matched set requirement for dragonbone armor (or dragonbone ebonsteel mod armor), too.
making the enchantment leveled (and able to be re-leveled by the various methods provided in mods) would also help preserve balance, so you don’t end up with some iron-armored noob prancing about with what is essentially an amulet of Talos and a permanent elixir of destruction in a hair-only slot with more armor than they should have at that level.