Flight sims are pretty much dead. So is the whole Battlezone type genre, where RTS and FPS mix.
Before they're buried completely, let's have a mix of the two.
BZ 2 is a B minus rated sequel to highly acclaimed Battlezone, a vehicle FPS + real-time strategy game. Build a base, grab resources,
build units, send units and yourself into battle.. with yourself controlling a vehicle. More of a vehicle sim mixed with a RTS than a FPS. You could also go into a "satellite view" and get into your God-mode view.. like Starcraft. Send troops here, attack this, defend that.
One of the biggest probs with BZ2 was that no one could really get into its combat. There wasn't a very easily discernable form of tactics you could develop for the game... the fighting itself wasn't immersive, like your typical FPS or a flight sim. You simply shot at the other vehicles, or jumped off hills, distracted enemies, etc..
BZ2 also had pathing problems. the AI had a tough time moving around.
a Flight sim BZ2 could fix a lot of these problems. Build a base, gather resources.. build fighter jets, or bombers. Maybe an aircraft carrier, destroyers, etc.
Customize the loadout of your jets.. set their altitudes, waypoints, speed.
Send aircraft into battle. Hop into aircraft to join battle yourself.
Oil refineries could be taken over by sending a C-130 paratrooper squad or something.
Janes' Fighters Anthology had a "Base assault" mode that came closest to this concept (excluding all the online sims). There was no RTS element, and all combatants were player-controlled (3 vs 3 games, etc). You had to destroy the enemy's base.