Suggesting Theocracy as a possible governance type that can be fleshed out with the "Religion arc" is a good suggestion.
Suggesting City States as a possible governance type that can be fleshed out with the "Economy arc" is also a good suggestion.
Military Junta(or whatever a militaristic governance is called) is a good suggestion as well.
There are ways to implement many governance types by name and basic concept at least without having everything already available .. that's the basic idea of Dwarf Fortress, that things gets fleshed out as development of the game progresses.
Most of those are basically what is implied under starting scenarios. Aside from city state, which is basically what we already are.
We should also consider the differences inside the same kind of government: for exemple, republics could differ over which classes get to vote and/or get elected (in some, merchants and craftsmen get to vote, in others, only landowners get to power) and their internal working (is the leadership done by an individual (consul, mayor) or a body (directoire, ), and how is the nomination? Does a senate exists and, if so, who elect it?). Monarchy would be whether they are elective (who elect the king?) or whether they are hereditary (what is the laws of succession?).
Arguments over who gets to vote among the actual citizenry really only make sense if we adding in privilaged/oppressed economic classes into the game. While this may seem historically realistic, we have gay marriage even when homophobia might seem 'historically realistic' instead. If we don't intend to add in homophobia, or sexism, or racism why would we add in a disenfranchised class of poor people, where is the consistency in that?
The actual nature of the government structure itself is very much a hot issue however. As is the actual mechanics by which the democratic system itself, as in elections is going to work in general. I propose we use the loyality idea from
Corporate Personality/Values and apply it to elections. We would divide the population into two 'parties' and divide the election into two elections.
We the player *are* the government party, if we lose the election we lose the game. However the first election is the 'primaries', it is when our party internally selects a candidate to stand for mayor. The opposition party will then select their own candidate at the same time. Then we have the actual real election for mayor which pits our candidate against the opposition's candidate. How dwarves vote depends upon their loyalty, loyal dwarves always vote for the government candidate, disloyal dwarves always vote for the opposition candidate and those in the middle will vote depending upon the personal characteristics of the two candidates and how in the middle they are.
Democracy runs the risk of the player being voted out of office. However democracy has an advantage in that it increases the loyalty of all dwarves THAT CAN VOTE, which reduces the chance of an uprising being launched against you, since the disloyal are fewer in number.