That kind of "supervillains" should be the Nomads. Ok, they shouldn't appear with huge fleets but they should be the Unlawful evil of the game, like they are also now. I'd suggest also a thing where Nomad players could have the skill to command some NPCs fleets and "create" their own events using themselves like "Event Boss" at the end. Who should use "Supervillain roles" should act like a "Dungeon master" in a "Dungeons & Dragons" game.