I agree the political spectrum should play a greater role both in diplomacy and in controlling domestic policies. I think they need to make it clearer what the three forms of popular support (ruling party support, dissent, and national unity) really mean.
National unity should be a lot like war-exhaustion in other paradox titles, essentially the willingess of the people to continue the fight. In democracies, the population can still firmly support the war while not supporting the party in power (the UK in '45) while in Germany and the Motherland many people were more willing to fight for the country rather than the leader. The distinction will become important in how you try to force a peace treaty. NU/WE can be sapped by convoy raiding, strategic bombing, loss of core province VPs and MP losses in general, largely as in Hoi3. Perhaps losing capital ships, especially the Pride of the Fleet could also be a hit. It would certainly make more sense than a hit to dissent as it is in Hoi3. The inverse where applicable is also true in all these cases, i.e. adding NU. In general though, it is far easier to lose unity than add it.
Dissent, or perhaps more accurately militancy, should be the general willingness of those opposed to you to take up arms or otherwise act against you, including non-citizens. In this sense it should be the amalgamation of "dissent" and "revolt risk" from Hoi, and it is represented at a region or state level and not in the global UI. Non core provinces will naturally have a high dissent while core provinces are likely to incur dissent hits if your political support is very low. It would be represented a percentage but not one necessarily linked to actual likelihood of revolt, but instead a graduated series of effects. For example: 0-10%: small drop in industrial/resource/leadership productivity, 10-25%: same as above + passive damage to infrastructure/naval bases + potential political event prompt(strike, popular demands etc), 25-50%: same + chance of forming underground cell (akin to Hoi3, possibly loyal to exiled gov) + passive attrition to occupying units, 50%+: same + chance of forming partisans in addition to those organised by the underground. Basically it would make it possible for a lot of the revolt dynamics already present in Hoi3 to affect core provinces if they seriously mishandle their policies.
Ruling party support should represent the trust people have in their leaders (and to some extent you). It should largely depend on domestic policy and not as much on the conduct of the war itself. Thus domestic policy and political management should be a significant part of peace-time gameplay, something that I don't think is unwarranted as most players spend at most a minute at the start of each game selecting laws and ministers and make only minor adjustments from there on. Minister selection should be the main focus here (and the DDs show promise here), with each minister you select allowing the implementation of 2-3 policies, with different policies depending on personality type and ideology. This is similar to previous titles of course. Unlike previously however, minister bonuses are not implemented immediately, instead you may activate policies using political points (like Monarch points in EU4). Political points are accumulated based on ruling party support and the number of cabinet ministers who belong to your party. Balancing your policies are the key to success, some policies will be purely to add party support, but will cost you in cash and eat up the number of potential policies you can enact(like welfare programs). Others will provide powerful bonuses but may damage party support(like conscription) while some will provide one time hits to support but will consolidate your support in the long run (like censor ship or banning opposition parties). Support can also be sapped by political decision prompts (which could easily be scripted to occur more often during peacetime) which may also force you to fire ministers or implement certain policies etc.
Consolidating ruling party support should be a critical part of your strategy, both as a dictator and as a democracy. Low support for the ruling party should negatively affect national unity and dissent and so a good base of support heading into a prolonged war is critical. There should also of course be diplomatic affinities between ideologies. This combined with the greater potential for shifting internal politics could make for very different, yet still historically plausible bloc positions heading into the war, or emerging from it.
As a side note, a more in depth political sphere could make a game more interesting from different start dates (either post versailles or post potsdam).
As usual that was considerably longer than it was intended to be; apologies.