Being that the Boomerang was in the last plane poll, HTC seems to disagree. I for one, would be happy to add it to my stable of 40 ENY favorites.
As for the OP, my guess is the Beaufighter and the Pe-2 for new planes. Hopefully a remodeled F4F-4 (and F4F-3) and FM2 or new 110s, too.
If it's a remodel of the F4F-3/4, I am hoping that they are put into SEPARATE airframes. There is enough of a difference to warrant it if I recall correctly. 3's had greater range and maneuverability while the 4's had greater armor and firepower.
I think the next addition will be another Soviet plane, but this time a bomber. I would put bet on it being the Pe-2, though I hope for the SB-3. Another addition I bet on is the TBD Devastator. Why? Because I can.
A serious 2nd bet would be the Beau as another addition.
For remodels I am betting on the B-26 to be remodeled. Hopefully we'll see a remodel of the SBD, D4Y, B5N and TBM as well.