This is what I'd like to see in game within 2-3 years... my decisions were based on the country's involvement in WWII, the importance of the plane in that country's airforce, and a bit of a 'novelty factor' when it comes to biplanes etc...
France: wasn't in the war for very long, obviously. However;
D.520; Did fairly well against invading Axis forces, particularly the Italians.
Italy: Italy played a comparatively small part in WWII; even less than I first thought, now that I've read more literature on the Regia Aeronautica's involvement in the war. Still, they deserve a bit more than 2 aircraft. I would like to see;
SM.79; Italy's workhorse transport & bomber
CR.42; One of Italy's main fighters surprisingly far into the war. Plus, it's a biplane.
Britain: Britain's planeset is fairly well filled out, however there are two aircraft that are definitely missing;
Beaufighter; From what I've read it was a fairly important and well suited ground-attack aircraft.
Blenheim; A BoB British Bomber that could be caught by the Bf.109E4 (the Boston III is faster).
Germany: Another country with a fairly filled out planeset, but is still missing two aircraft that played a major role in the war.
Ju52; Iron Annie. Served as a bomber in the very beginning of the war, and was the Wehrmacht's workhorse transport through the entirety of it.
He111; Major German BoB bomber. Slower but better armed than the Ju88.
Personally I would like the Bf.109G6/AS or Bf.109G10 as well.
Japan: Missing some planes here as well.
Ki43; Early war Japanese land based fighter.
A6M3; Mid war Zero. Our current Zero set includes a 1941 and a 1944 version with nothing in between.
D4Y; Mid/Late war dive bomber.
Union of Soviet Socialist Republics: At the outbreak of the Great Patriotic War, the VVS was one of the largest air forces in the world, despite being hopelessly out dated. The USSR played one of the largest roles in the downfall of Nazi Germany, and the VVS is very poorly represented considering. In fact, we don't have any home-grown Soviet aircraft until the late 1943 Yakovlev 9T!
I16; Most common fighter in service at the outbreak of Barbarossa.
Yakovlev 1; Earliest Yak, the best fighter in service at the outbreak of Barbarossa.
Yakovlev 7; Next in line, followed by the Yak9.
Yakovlev 3; Ultimate evolution of the Yakovlev series of fighters.
35,000 Yakovlevs were built in all, meaning their production number was second only to the Ilyushin Il2.
Pe-2; Russia's main tactical bomber.
I attempted to make this list based on what was really missing from the game without any bias. I'll never end up flying anything on this list beside the Ju52 and the He111 but everything here is a major hole in the planeset.