Air warfare is fun but is pretty simple - spam vamps or maybe avengers to get air supiority. Tridents add another element, and air seems well balanced now (except Licho) but it still feels that air warfare could use something more.
Air warfare could use a third AA unit to create a "rock paper scissors" game. Vamps can slaughter avengers, the new unit could slaughter vamps, avengers could slaughter the new unit. The new unit could be more powerful and better range than vamps, but be innacurate and have trouble hitting avengers. Or it could have slow-moving flak projectile that avengers can dodge better than vamps due to lack of a firing slowdown. Or if those ideas don't work, some kind of AA e-war. Units could be different speeds to make micro neccessary and mixed air aa death balls difficult.
The air game is well balanced so I expect we don't want to change it unless we decide on a good tweak, but the factory could probably fit another unit or two without being overcrowded.
Other random less serious ideas for air fac
-Bomber with slow-damage and v large AOE and small push effect
-Make Licho dedicated strat bomber, remove AOE and give it non-tracking high damage precision bomb instead. Reduce in cost.
-Make shadow into effective anti-mobile by doubling dive speed, or making bomb track, but reduce hp further.
-Make a high speed bomber that fires a brief heavy machine gun volley then reloads, less cost-effective than napalm, but more survivable if they have mobile aa. Make HMG sound more like a HMG :)