If the game were to have a 1939 start date, you would have a lot of extra countries to have units for. Here’s what comes to mind just off the top of my head:
ALLIED or Neutral but attacked by Axis
Poland
Norway
Denmark
Holland
Belgium
Yugoslavia
Greece
AXIS
Hungary
Bulgaria
Romania
Finland
Those are just for Europe. If you include the Pacific, I think Burma had an army so they would be Allied or Neutral. Thailand was Pro-Japanese.
Even though these minor nations wouldn’t need the whole range of different units like you mentioned in your original post, most would at least need a sort of basic set of pieces (infantry, artillery, tank, fighter plane, medium bomber, transport ship, submarine, destroyer, and cruiser). You could probably do away with capital ships for the smaller nations. Also, for the land locked nations you could probably do away with ships all together. Even so, that would be a lot of different new pieces in many colors.
Then again, WOTC might simply have the minor nations just share sculpts of the bigger nations just in different colors (German sculpts for Hungary, Romania, etc. and British or French sculpts for Belgium, Holland, etc.)
If you get into too many new sculpts, that will surely jack up the price and at some point, it will be cost prohibitive. Either it will simply cost too much for WOTC to make the game or if they do, they will have to price it too high for people to buy it.
That being said, it does sound like a very interesting project. I am wondering about the political situations. Could you make different choices?
Like could Germany decide NOT to invade Poland first thing and instead go after France?
If Germany does invade Poland, Will the Soviet Union also invade Poland?
I ask this because WW 1 basically started when Austria/Hungary invaded Serbia. In Axis & Allies 1914, they force you to invade Serbia as Austria/Hungary round 1 and that gets the game started. Whatever else Austria/Hungary does, they HAVE to attack Serbia. So, in a proposed Axis & Allies 1939 game, would Germany be forced to invade Poland first thing? OR could they take another course?
I’ve always been fascinated by the “What If” scenario.