Hitech once set an order of base capture that we had to follow to win a map with arrows on the map showing the order of feilds. Not around anymore is it.....
I seem to remember the AvA guys tried this out some years back.
Being an AvA enthusiast, there might have been some sort of order of capture in order to get additional equipment or to win the 'scenario'. That is NOT the same as keeping vehicle bases of the chess piece's origin active (by making them uncapturable).
Another option would be to set the capture ability of vehicle base(s) on the the capture of specific Air bases and or towns. 
Jimmy, that still 'closes the door' to nearby attacks on 'behind the lines' acquisitions. It might cut down on the loitering time at vehicle bases, but
I am looking for an overall effect of increasing air combat while still having a very active roll for ground vehicles to recapture airbases that have been surrendered.
A little back story. There is a certain map(s) in which certain ground bases have spawn points across a broad body of water from each other. No one questions how do those ground vehicles "spawn" there (I mean were they air lifted, shipped, or somehow smuggled up the coast). In any case, those vehicle bases are targeted to get a foothold on another chess piece's shore. This can go back and forth, stalemate, or eventually give way to a flood of captured territory.
Making airfields the only property that changes hands,
keeps the balance in check and reduces the milkrun base captures during off hours.
Not that I am looking for anyone to agree with the idea, but I would just like to know that I am stating the objectives clearly enough.