The Avenger is probably overkill anyways for modern warfare. At this point its advantages over a lighter Gatling-style cannon were probably more psychological than physical - the enemy doesn't have tanks.
I could see the US military fielding a drone built around a 20-mm Gatling gun to fill the void left by the A10, if they really felt that bullets were better than Hellfires for the role.
> if they really felt that bullets were better than Hellfires for the role.
Well, Drones currently carry a single hellfire (at best), the unit cost is $68000 and the anti-personnel version is pretty nasty (it's a thermobaric warhead). A gatling-type cannon provides better precision, more staying time and much cheaper (even for the A10's 30mm, rounds are ~$750 per hundred for HE to ~$1300 per hundred for DU, 20mm rounds are $300 per hundred for HE to $500 per hundred for SAPHEI, you can literally get a truckload of high-caliber rounds for the price of each Hellfire).
I could see the US military fielding a drone built around a 20-mm Gatling gun to fill the void left by the A10, if they really felt that bullets were better than Hellfires for the role.