I think the Gretchin are ready for a Republican model of government:
1. French Revolution - they overthrow Ork aristocracy and institute a reign of terror, until a shorter than normal Gretchin takes over the reins of power.
2. American Revolution - they expel Orks from some of their outlying planetary bodies and form a union pursuing happiness.
3. Russian Revolution - The Eldar brainwash a Gretchin with a goatee; he's followed by one with a moustache who successfully repels Imperium incursions.