The Ebon Hold is literally crawling with undead. The Death Knights are the masters of death itself. We won't get a necromancer. They would have to completely revamp death knights. Undead minions are a core for the unholy death knights playstyle and combat. Its a talent for frost death knights to summon a flying, dead dragon.
You say to have them as anti-paladins. They already are. Unholy death knights are all about undeath, rot and decay. Frost death knights are about the chill of death. Blood death knights are about using the blood and bones of their enemies. Doesn't get much more anti-paladin than that.
Before trying to get Necromancers as a thing, think of how you would change the entire functionality of a class. With warlocks, it was 1 ability from 1 spec that was lost. The rest of their tool kit was able to be revamped to be more about demons and less about the warlock turning into a demon for a short time. You want the entire tool kit of death knights to be removed when death is their thing. All of their tier gear has skulls on it even!