The problem with narrowing it only to planes that flew during the WW2 time frame, means it would include a lot of one off birds too. While I make no claim that HTC said they had to have seen combat. That does seem like a reasonable qualification as even at this point there are numerous WW2 birds that saw combat that we don't have in game. Think Oscar, Beaufighter, Pe-2 etc along with any number of different versions of Spitfires, 109s, P40s, Mustangs, and so on. Those seem more important to me because of Special events stuff that goes along with MA stuff.
If HTC decides to do Airwar 1946, then I think the birds that just missed it would make more sense and I'd hope for an arena dedicated to those types of birds, as you'd be talking Sea Furies, P80s, Tigercats, Bearcats, P51Hs Spit 22/24 and all those what if Axis birds.