The concept of an invincible being that destroys even Adminium doesn't seem like a legitimate threat at all. It sounds more like forcing you to delete your world when one shows up, regardless of when or where. Seeing how this is heading, they'll probably be hostile, have a huge sight range with x-ray vision [see through blocks], and ignore things like light, difficulty, even the game mode. It'll probably take a mod to disable their appearance, too.
At this rate they should probably be called (Ender)Dragon Gods instead of just (Ender)Dragons if you get my drift.