If the Mythic armour sets are indeed non-canon and are part of some What If…? branch of the Halo Universe, I reckon Hal’s armour from Fable II would be a great addition to the game.
I guess there wouldn’t be any licencing issues given that Microsoft have the rights to both Halo and Fable. It would probably have to be modelled from scratch, unless Lionhead still have some assets floating around.