I've been thinking a bit about how this could work.
Lets say every 30 minutes or so a bombing raid spawns at one of the three uncapturable airfields and heads for a random strat target, raid targets alternating between the other two countries. A message appears on the opposing country's "HQ" radio channel i.e.:- "Intelligence reports Knight bombing raid heading from A6 to our radar factory at 10,6,1, ETA 27 minutes". These messages get updated periodically with the raid's position and ETA, how often could be down to the state of the country's HQ. Ten minutes later a raid spawns at one of the other two countries and so on. Air spawns are not really going to work in the MA due to the risk of a raid spawning around a player just as he was flying past (imagine the whining!).
The makeup of each raid would be down to the numbers of players online at the time the raid spawns. For instance lets say currently Bish have 100 players, Knits have 50 and Rook 25. In this setup a Rook raid might have B-29s or B-17s escorted by P-51s or similar, the Knits might get Lancs escorted by Spit 9s and the Bish might only have G4Ms escorted by Zeroes. Similarly AI player quality might drop as a country's player numbers increase, so in this instance the Bish raid might be mostly AI rookies and the Rook mostly AI aces. Perhaps the Knit raid might climb to a higher altitude and have more aircraft than the other two as well. Think of it as each country's resources being spread between all its aircraft, both AI and human. So less human players means more resources can go to the AI raids. This might give players an incentive to switch to the less populated countries so they can attack the easier raids.
The AI fighters would be mostly close escorts who break off to stick with the bombers if an attacker dives away, with a couple of detached escorts who don't. Those players who consider AI raids in the MA to be the spawn of the Devil or some kind of Commie plot can simply turn off the HQ channel and ignore them. The AI fighters wouldn't attack until well inside icon range so if you run into a raid by accident simply turn around and fly away.
I can't think of anything else which would bring players back to the game outside of US peak hours more than this. I would much rather fight humans than AI, but AI is better than nothing and that is currently my only option. The ability to either intercept or escort such raids would make them focal points for other A2A combat oriented players as well, so human v human fighter combat becomes more likely, not less, with this addition.
Lastly I am not sure the option of being able to jump into an AI bomber's gun position is such a good idea. I can see this being gamed, with a player using a second account to shut down the bombers' defensive guns as he attacks.