I would like to see a failure cascade when a aircraft takes crippling damage. For example the loss of a strut causing other components to loosen and break on a targetted plane over the next 10-30 seconds. Damage exacerbated if the aircraft maneuvers heavily.
Heat-of-battle psychology: Maybe pilots who bail from perfectly good aircraft when there's an enemy on their six due to the fear and panic. Also, it would be nice if pilots had some kind of a morale level dependent on how many of them are involved in the dogfight compared with the number of enemies. A bomber formation that encounters a large interceptor force might just ditch bombs and turn for home. The last few outnumbered fighters in a dogfight may try to disengage - focusing on defensive maneuvers while they head homewards.
Some of this psychology stuff is less important in BOB than in other SOW releases, perhaps? It'd be nice to get it into the game early though.
Another related idea is to have some missions give a bonus to pilot morale. The briefing could have a "This mission MUST succeed" element. A flag is set that gives the pilots greater moral strength and willingness to take on the odds. The mission objective is vital, so Bombers will be more likely to press on into danger. Fighter pilots will be more willing to fly into massive formations of bombers and escorts. To a certain extent this mission flag will be a given when the mission is "Homeland Defence", so the RAF in BoB (and also the Polish Airforce in 1939 and the Luftwaffe of 1944, given other scenarios) will be given the aggression their role requires. Apart from the odd LMF of course.
T.