mabye you could work on new units that make the game feel more... WWII ish.

Planes...planes and for germany panzer to replace tanks. And a bigger map plz, so you can fit infraty in there.

change france and poland into city states that are permanetly at war with axis powers

Make a Canadian Civilization apart from the UK

More units, new nation powers, make city-states as smaller European countries, change names of naval units to "classes" (ex Yorktown Class, Fletcher class,) and maybe add differnet time frames to start (1939, 1943, like Hearts of Iron 3) and maybe make smaller scenarois for battles (Stalingrad, Kursk/Operation Zitadele, Kharkov, Siege of Leningrad, Normandy, Fall of France, Midway, Anzio, New Guinea, Ichi-Go, Burma, Operation Market-Garden, Siegfried Line, Battle of the Bulge ect..) and names of regular units ( Germany AA= Flak Vierling, Russian tanks= T-34)
You could also Get Idas from books and video games (yes, I know a lot about the subject, sorry for my wordy comment)

Could you have it so the game wont go past the era it starts in so you don't end up with future units?

1 bigger map or more space :) 2. Make a real Poland 3. Few city state

Country of Luxemburg

Australia would be a wonderful addition to the Allies. Since it was a big part of the war against the Japanese in protecting Indonesia, Papua New Guinea, and the Solomon islands.

Greece
Leader Ioanis Metaxas
Unit Evzones
Abillity Metaxas Line When defending near border more deffence + life