Adding a bunch more systems means a TON more balancing and bug testing. Look at how long it took to get HoI4 ready, it'd probably another 6 months to a year if they added in Vicky style economics. That's 6 months to a year where they are spending money instead of making it. Paradox isn't a AAA developer and HoI isn't a AAA series, they aren't making CoD money with their games and they aren't reaching a CoD audience.
Speaking of that making the game grotesquely complex does not, in fact, increase the size of your audience. It actually reduces it. For everyone that wants to combine all the mechanics of every Paradox game into one there's 5 people that will go "Holy shit that's a learning CLIFF, not a learning curve." and bail.
hypothetically, to make a cold war game if based on using some of the mechanics from viccy2, hearts of iron, perhaps even that of EU4 isn't hugely complex, tbh EU4 mechanic wise is practically just shy of having everything to make a decent cold war game, it just lacks the essence of HOI focus on combat, the difficulty would be in setting the tone & atmosphere of the cold war period, with artwork, historical nods to events throughout the timeline, and research on historical leaders & there alternatives, but that could be generically managed, since EU4, Viccy 2 and CK2 diverges into an alternative reality the moment you press go, HOI3/4 being the only exception were the AI tries to strictly follow a relevances to it's historical counterpart, which also make's it quite predictable if you have historical knowledge and hindsight. EU4, Viccy2 & CK2 ai will adapt diplomatically & militarily to your actions making it more flexable, somthing that would be easier to implement then having a fixed storyline like that of hoi3/4 that are very difficult to drastically change, although for hoi4 there is an unhistorical mode, which i'd imagine will maintain it's novelty.
Viccy 2 and EU4 economics are extremely straight forward, practically automated with the rest being common sense and logic, the populaion demographic/culture can in both be manipulated or guided but aren't again difficult to learn, the only place i might share your concern where it may become a bit more hands on is the combat aspect of it while managing the other aspects, but with the new hoi4 army control system, it lifts that burden somewhat, also not to mention, in the cold war there won't be has intensive drawn out huge periods of war requring you to check multiple frontlines, but generally a couple of hotspots at most, with the main focus of geopoltical shifts resulting from soft power, diplomancy, coups and special activities division (SAD)
I don't really see it being over complicated, perhaps difficult for those who aren't familiar with the period, and therefore feel overwhelmed by what they should be doing in order to achieve victory? Since most wil probably want to turn the cold war hot, which should not be the main focus of the game, but instead appreciate that conflicts between great powers have changed drastically away from conventional warfare and into more proxy efforts of dicking each other over to achieve there geopolitcal aims, which is still true today.
It would probably be the only paradox game to play completely differently from the rest of the franchise where painting the globe your faction colour would not work due to initiating MAD, and would be closer to viccy 2 sphering puppets mechanics without the conquest & colonialism aspect in it fullest. Sure it will be niche, since most of the general public don't have the same amount of knowledge on the cold war as they do other periods that are romanticized, and could be risky to try such a period for that reason, but i don't think it being over complicated in the sense of the mechanics invovled would make it a steep learning curve.
