50 years from now, the skies will be empty.
Flying fighting will be down at the tree tops, with unmanned drones. Fleets of thousands of them doing close support operating against any troops caught out in the open, plus knocking each other down.
Any plane that enters an engagement zone would have to avoid radar, thermal, RF, Magnetic, and who knows what other types of tracking. Mass-based? Missiles will get so sophisticated that they'll be able to disregard any amount of jinking and countermeasures will be ineffective.
Counter-missile defenses will evolve in-step with this, and eventually the missiles will be mostly neutralized, but will then be replaced by the next step:
First, let me preface this by suggesting that MBTs and Artillery will be combined into the same vehicle. All of the tanks/fighting vehicles in the theater will be networked together. Any aircraft entering the zone would be tracked by ground units who would instruct any units ahead to fire inert or fin-guided rounds to intercept the plane. Inert rounds would be able to take out level flying planes without triggering their missile detectors (no thermal bloom), rounds with fins for terminal guidance would be able to deal with maneuvering targets. Again, no easy IR detection of the incoming rounds.
Out over the water, maybe there'll still be room for fighting, but even then, I'm guessing swarms of drones.