Hmm...They could have added a MiG-3 for the hell of it, and could have also (rather than Korsun) put Leningrad in place for a map. Maybe a Fokker DXXI because I think they look cool and are interesting planes. They could have added at least some French fighers like the MS402 and D.520... under estimated fighters I tell ya!
For all the nations represented in BoP, here's one (or two) planes they could have added.
Italy: Fiat CR.42 or Fiat G.50
Germany: Ju-88 or Do-17
US: F4F Wildcat or P-38 (P-38s played more of a roll in Italy, than a P-51 did.)
UK: P-40 or Gloster Gladiator (It's really surprising for a WW2 Airplane game, to not have added MALTA which was nothing but an aerial combat zone.)
Russia: They could have added the LaGG-3 into BoP instead of the useless Po-2.