This is something that would definitely be cool to see added.  Airfields would basically be like CVs (and could be disabled too) only they could launch much larger aircraft such as heavy bombers and land-based fighters.  Airfields could be disabled by bombing the runway and hangars, however they can be repaired since they have DP.  When an airfield's DP reaches 0, the airfield is out of action for good.  Here are some planes that could be operated from each airfield, the nation depends (of course) on what nation the harbor is in.  Also, airfields would use pilots, so basically whoever gets control of the airfield (should be set before battle) gets to adjust their plane arrangement and what pilots they are using.

USN Fighters:
P-47 Thunderbolt (T4)
P-38 Lightning (T3) 
P-40 Warhawk (T2)
P-39 Aircobra (T1) 
USN Bombers:
B-29 Superfortress (T2)
B-17 Flying Fortress (T1)

RN Fighters: (I know a lot of these are ingame, but there were land-based versions of them)
Hawker Tempest (T4)
Supermarine Spitfire (T3)
Hawker Hurricane (T2)
Gloster Gladiator (T1)
RN Bombers:
Avro Lancaster (T2)
Handley Page Halifax (T1) 

KM Fighters: (again land-based versions)
Focke-Wulf Ta-152 (T4)
Focke-Wulf FW-190 (T3)
Messerschmitt Bf-109 (T2)
Arado 197 (T1)
KM Bombers:
Heinkel He111 (T2)
Junkers Ju88 (T1)

IJN Fighters:
Ki-84 (T4)
Ki-61 (T3)
Ki-43 (T2)
Ki-27 (T1)
IJN Bombers:
G4M Betty (T2)
Ki-21 (T1)