-Will there be compulsory vs non-compulsory voting? Non-compulsory voting makes elections about raising the plurality of one group and lowering that of another, whereas compulsory makes it about changing the issues and what not.
There kind of already is. With consciousness low pops will vote for the incuments. This pretty much simulates pops not bothering to vote.
Pref. vs. first past the post? Likely what is in Vic1 is first past the post, since that's how the British electoral system works. However I think it's too much of a complication. What would the result on the game be? As far as I can see it'd result in perhaps a different party coming to power, or maybe not. In real life proportional representation means that parties which should not get into power get a few useless seats to make sure that the party in power can't get anything done....

Much of your ideas, and I don't mean to offend you, but I feel they add a whole new level of unnecessary and unimplementable complication.
One very important thing you did hit on is Constitutional Monarchy.
Victoria seems to think a "Democracy" is more democratic than a "Constiutional Monarchy". I think we can all accept that is not the case. The most democratic counties in the world right now are constitutional monarchies. As far as I'm aware Scandinavian countries typicaly come top of any assessment of democratic quality.
So in Victoria 2 I'd like to see the style of governement correctly stated. But there's room to state it's a Constitutional Monarchy, Democracy, or Dictatorship, regardless of how the nation actually works.
For example it's fairly possible to imagine a country with a hereditory dictator, where things are very democractic. The Dictator's family functions much like a Monarchy in modern times. The reasons to distinguish between Democracy (i.e. no hereditary rulers) Dictatorship (i.e. a different dynasty than the country started with) and Constitutional Monarchy (the dyntasty the game started with) is to first of all have a bit of flavour. It's interesting to know that the Hohenzollern dynasty is in Prussia (we'd know if it was a const. monarchy) or that the current head of the UK is not of the Windsor dynasty, but something akin to Cromwell. Additionally this would greatly influence events. A random coronation event could fire if there is a hereditory leader, or be prevented from firing if there is not. Flavour events when a monarch dies may or may not fire depending if this is set or not.
Additionally, this change would also get rid of the false split a monarchy faces in Victoria. It either goes Democratic or Constitutional Monarchy, and there is no chance to change afterwards. With this change in place the actual form of government would change, rather than one ambiguous header.
For example we may see...
Prussia
Constitutional Monarchy
Head of State unelected with full veto.
Elected Parliament
Suffrage - Wealth
United Kingdom
Constitutional Monarchy
Head of State unelected with limited powers.
Elected Parliament.
Suffrage - Landowners
Bolivia
Presidential Dictatorship
Head of State unelected with full powers.
Ministers directly appointed by Head of State.
Suffrage - None.
United Provinces of Central America
Presidential Dictatorship
Head of State unelected with limited powers.
Elected Parliament.
Suffrage - Men
United States of America
Republic
Elected President
Head of State elected with limited powers.
Elected Parliament.
Suffrage - All
Sweden
Constitutional Monarchy
Head of State unelected with no political powers.
Elected Parliament.
Suffrage - All
I hope that gives a bit of an example of how I'd like to see things working. Notably that there would be no democracies, states in Vic1 which were called Democracies would be called Republics.