Flak cannons are a little different than a shotgun. They explode into shrapnel once they reach the end of their fuse. They're more similar to a grenade launcher than a shotgun, imo.
I think a comeback is unlikely though. The travel time of shells combined with the agility and size of drones would make them very hard to hit. They work really well on large targets because (like a grenade launcher), anything close is "close enough". They were a good counter tactic for the relatively slow and lumbering B17's; they're easy to lead and there are important components everywhere. Drones are tiny and fast; the important bits on a B17 are much larger.
I wouldn't be terribly surprised to see something akin to a flak cannon that fires EMP shells, though. Flak cannons reduce their coverage over range as a matter of expansion. EMPs do not, and are only limited by the amount of energy we can pack into a shell/rocket. Rockets are honestly probably a better choice, because they can "track" the swarm if it tries to take evasive maneuvers. Shells don't really have that option.
Worst case scenario, nukes can be used as an EMP. We did make nuclear artillery shells for a time, though I'm not aware of an anti-aircraft EMP variant.
I think a comeback is unlikely though. The travel time of shells combined with the agility and size of drones would make them very hard to hit. They work really well on large targets because (like a grenade launcher), anything close is "close enough". They were a good counter tactic for the relatively slow and lumbering B17's; they're easy to lead and there are important components everywhere. Drones are tiny and fast; the important bits on a B17 are much larger.
I wouldn't be terribly surprised to see something akin to a flak cannon that fires EMP shells, though. Flak cannons reduce their coverage over range as a matter of expansion. EMPs do not, and are only limited by the amount of energy we can pack into a shell/rocket. Rockets are honestly probably a better choice, because they can "track" the swarm if it tries to take evasive maneuvers. Shells don't really have that option.
Worst case scenario, nukes can be used as an EMP. We did make nuclear artillery shells for a time, though I'm not aware of an anti-aircraft EMP variant.