Only Monarchy and Despotism (but all Civs start in Monarchy already).
Possible explanation: The Conquests were designed and balanced before Feudalism was introduced; no Conquest features any of the new Govs, especially not the Xenophobic concept, regardless of how the Govs are named in the particular conquests.
And seeing that Feudalism for example had a last-minute-change, it looks like a good idea.
And anyway: Do you really miss Feudalism in the conquest?
And considering 2/3 of the Civs are REL, this would seriously hamper the few that aren't, since everyone else could permanently switch between Monarchy (pay) to Feudalism (huge unit support). IMHO, that would kill that great conquest, since it is a clear exploit.