Some countries will start the game already under Constitutional Monarchy, Great Britain for one.

I wonder whether Constitutional Monarchy might be a third option when Republican sentiment is starting to boil over, in order to appease the masses without losing the loyalty of the aristocracy. As you say though I'm sure there must be some penalty for such fence-sitting.

Given what CA have said about having a separate tax rate for the ruling classes and the masses, I suspect that much of the government and taxation aspect will be about trying to please both groups at once. Kind of like RTW's balancing act between pleasing Senate and People (only in reverse I suppose, the tendency being to move toward rather than away from a Republic as the game progresses.)