I remember that part of the MBT-70 design had a 20mm coaxial gun to deal with infantry, LAVs and other soft targets as to not waste main gun ammo, the BMP-1 and other vehicles carrying antitank missiles made the designers realize that regardless of overkill the tanker would use the main gun to deal with those threats at max range so the idea was dropped.
But yeah, any kind of secondary autocannon for AA work is going to be impractical due to the required gun elevation vs size of the turret, not to mention the targeting systems required for locking on small, and relatively cold aerial targets such as drones vs land vehicles. Frankly the ideal solution would be dedicated AA gun-missile vehicles both tracked and wheeled to support combat formations, but is too expensive and resource intensive to be done without some impressive evolution of the current doctrine and related budget.