As Greebo mentioned, some mid-war common aircraft are missing that would be invaluable to AvA, FSO, Snapshots, etc., but probably wouldn't be as well received in the LW arenas.
These would be, specifically, by country...
Ki-43
Ki-27
G4M
Yak-1
SB-2
Pe-4
SM.79
C.200
G.50
He-111
Ju-52
Beaufighter
Blenheim
Wellington
These aircraft would pretty much open up the 'historical' areas of AH, AvA, FSO, Snapshots, etc.
While I understand that most of these aircraft would never be used in the LW, there's certainly a valid argument for having them.