1. Lockable tailwheels for the planes that had them? I'm not sure which ones did...
2. Ground wreckage of the planes just shot down? If only for 5-10 minutes as a burnt, smoking mass smoldering down to char...
3. Better simulation of ejection. Popping the canopy and jumping was not instantaneous. Perhaps a timed delay based on the pilot's situation (wounded), G forces that are holding him back, or even not able to eject at all.
4. Bombing effects that crater the ground and actually affect the ground (airstrip cratering, making pilots maneuver around these obstacles.
5. Repair of minor airframe damage. We now get unlimited fuel and ammo from rearm pads. What if our FE can remember the last plane and damage we took and offer repairs at perk costs? Everything from flaps, ailerons, elevators, props, tire replacement, cockpit glass, oil leaks etc...
6. A mobile flak or artillery installation for extra perimeter defense of a valuable target. Also the ability to time the detonation of flak to altitude for high flyboys.
I'm just trying to think of ways to spark some ideas to progress the game further...