Internal Politics: I want more reforms and more options between them, as well as more reforms which will not be incremental. Electorate reforms should also have options for specific pops to vote only, like military leaders only, religious leaders only, military/religious leaders and military personnel/religious personnel (more on that below).
Dynamic Political Parties: they should be more dynamic, shaped by their ideologies of course but also the conditions surrounding them (if a pro-war/protectionist/planned economy/atheist communist party takes control of Russia for example, countries that like Russia or are in its sphere of influence might see their communist parties adopting closer stances to that party in an attempt to achieve similar success), this system will make politics less predictable and more realisitic I would say, showing that the alt-history stuff that can happen actually has an effect on the game. Of course for this to happen, the stances would need to be greatly expanded. The names for the parties could still be taken from a pool of historical names but appear randomly and with dynamic stances that might differ from their historical counterparts (except for maybe the first party of each ideology which could just be the first party of that ideology as it appeared in the history of that country). This could even be an optional gamemode for those who want the historical parties strictly, like the options in CK2 and HOI4.
Dynamic Reform Stances: Instead of static enact/revoke stances. The parties could also have a sort of support meter. For example, a conservative party might be okay with granting the lowest form of unemployment subsidies but might be entirely against any healthcare funding. If militancy is high enough, it might force them to conceed to the lowest possible amount of healthcare or to back an increase to unemployment subsidies that is 1 change higher than their previous support limit, but no further. Effectively, apply the militancy mechanic to every issue and for most parties. The more ideologically rigid movements (fascism/communism) would have the added benefit of not really caring about militancy and would need a really high amount to be forced to back down on an issue and only 1 point down or up incrementaly.
Radicals instead of An-Caps: Anarcho-liberals as they function at the moment should be replaced by the historical radical whig and jacobin-like movements they are meant to represent instead of anachronistic anarcho-capitalists they end up being. Effectively more radical liberals in their outlook, not as supportive of social reforms as socialists but not as relunctant as liberals. leftist liberals effectively. There could be some sort of oligarchic ideology to represent something similar to the current anarcho-liberals but I can't think of anything specific.
More government types: Oligarchy should a government form that represents systems where multiple executives rule in a council that is elected only by some strata of society (I cannot quite figure out mechanics to make it stand out from just wealthy vote only democracy - I guess if only the wealthy can vote then this government is in charge and it becomes a democracy if the laws expand the voting franchise), it would be comprised of that specific class' ideologies. Military dictatorship should be possible, with officer pops and even soldier pops being the electorate (again depending on the franchise law). Presidential Dictatorship should be modelled more closely to the republican dictatorships of EU4 and be effectively an one-party state for ideologies that are not communism/fascism/radicalism, it should come about in the same way as its EU4 counterpart, a democracy is eroded to the point where it shifts to it. There could even be a theocracy goverment to represent certain middle-eastern political movements and the government of several european countries, like some of the clerical states of the former HRE and the Papacy. The electorate for them would be clergymen or even a new "high priestood" pop. Each Party could even have an best government stance which would make it easier to switch to that government or would even lead to coup events where that party tries to overthrow another and take power if there is enough militancy in their supporters.
Dynamic Ideologies: The ideologies we know today as liberalism or communism or conservatism are not set in stone and back then they were just being formed and many of their thinkers either left them to found new movements (like many communists now being seen as anarchist thought leaders or many liberals being considered proto-socialists) or didnt gain enough traction within their movements to shape them in the direction they wanted. This might be a bit too ambitious even with modern technology but maybe the ideologies could shift based on the circumstances and the thought leaders forgotten by history or considered secondary could become the primary influencers of their movements and cause a radical shift in the ideology compared to how we know it now. I consider this my most ambitious idea here, if this system ends up too complicated then my other suggestions would suffice.
These are the ones I can think of right now, if I happen to think of any others I will come back to the thread. If anyone thinks they have an idea to make these better or wants to discuss this, please quote me and tell me.