I've been kicking around an idea for a setting for a few months now.
Skies on Fire: Aerial warfare in an alternate world roughly at the same tech level as modern earth. Basically think movies like Top Gun, or games like Afterburner or Ace Combat. The game will focus mainly on war stories and the occasionally gray morality soldiers face in a prolonged and bitter war.
Obviously vehicle rules will be needed for this. I don't mind building the aircraft from scratch and so forth, but having to do that and hammer in some vehicle to vehicle combat rules is more than most anyone has time for...