Is this the biggest update a Paradox game has ever gotten? I am really impressed and thankful for the team's hard work. If HOI4 continues to get updates like this then it will become a legendary game in time. I do wish more new music was added. I really like the radio station style period music currently in the game. That kind of thing adds a lot of immersion to the simulation. It would also be nice if the popup boxes were more immersive looking. Instead of just being a small generic looking box they could resemble period specific newspapers and military/government memos and reports etc. There's really not enough popups pictures in general and they're too tiny. You see the same ones again and again and again.
I would really love to have an advisor like in Stellaris. I love that feature of that game and HOI4 is so complex that it could really use one. I hope the next big update focuses on the submarine warfare/naval mechanics. Using submarines is currently a total micro nightmare and not worth it. It's just not possible to wage the kind of submarine campaign that Germany was trying to do against Great Britain. I also would like for the weather mechanics to be more in depth. Like a game option to switch between historically accurate weather or more random weather. A weather forecaster system to enable more detailed planning. The ability to control how your Divisions/Air Wings behave in certain weather. For example you may want to tell your German Panzers to launch a surprise night attack under overcast cloud cover...
The game really needs a fuel mechanic as well and maybe also a food mechanic. Starvation was a serious concern during the war. If your country doesn't produce enough food then it should have to be imported. If your country starts running out of food then it should cause instability and start draining your manpower pool. It should also make it easier to force a foe to surrender.
It seems to me like it would make sense to add more climate acclimatization for Divisions. There are a lot of different climates on the Earth so just cold/hot isn't detailed enough in my opinion. I'd really like to see a "Secret Missions" mechanic where you can attempt commando raids, assassinations, dam busting, and daring strikes like the planned Japanese submarine attack on the Panama Canal etc. I also really want to see a Commendations/Medals system for soldiers in Divisions. There were many brave and heroic soldiers in the war. I would like to know how many heroes are in my prestigious Divisions and how many medals they have earned and for what. These heroic individuals could give small stat boosts to Batallions/Divisions. Tank Aces must be in the game especially for Germany!