Destruction!!! (and post-destruction)
Okay, I'll be more specific:
-dynamic damage (not a scripted model)
-physical craters
-more bailing options
-random chance for failure, badly packed chute, poor quality, etc
-chute dm, based on fire mostly in fighters and attackers, but in a bomber would be affected if shot as well, for those that had chutes stored away from the ' men inside
-bail procedure, clickpit for things like canopy ejection and/or parachute retrieval, but also buttons to activate the chute manually
-better ejection seats, ones that have realistic parachute activation time!
-possibility for pilot injury outside the aircraft, whether by being shot or rough landing
-an incredibly small chance of surviving a fall from your aircraft sans-parachute, based on statistics and impact location
-realistic gear damage
-more realistic crashes
-no detonation without fuel or active bombs
-detonation that doesn't guarantee complete disintegration of the aircraft, if you've seen a CF-18 airshow crash from a few years back, that's a good example
-part of a true dynamic damage system, soft body physics/crumplycrumplycrumply