Sounds like a lot of work for being a class skin. They'd have to either add a necromancer class, redesign Unholy to be a proper "Necromancer in plate" that Blizzard called it as, or make Necromancer a 4th spec for either Warlock or, more appropriately, Death Knight to be a ranged-in-plate spec like how their talents in Legion let them do their dps from ranged before it got nerfed. Similar to how Holy Paladins are healers in plate.