The main problem I see is that reactivating all these old mothballed systems will require a lot of man power to operate and maintain, not to mention the costs of upgrading the systems. The ammo would also need performance upgrades to make it effective... proximity fuses and efficient air burst shells would need to be developed and produced...
I think adapting an existing system to fire new ammo would be the most cost effective solution... 152mm artillery units are already present in the current Russian military, so special air burst models with a laser to set their fuses in flight make a lot of sense... getting a huge number of old weapons with all sorts of different calibres out of storage and back into service sounds like the sort of reaction the US is trying to provoke.
The facts are that the Russians already have an excellent air defence network and it is getting better and better all the time... reintroducing a whole lot of old obsolete calibres and guns would not make things better... those weapons could certainly be given a small upgrade and sold to allies who don't need or can't afford anything more sophisticated, but with new EW systems and new airburst 57mm guns along with 30mm airburst guns and potentially 152mm air burst rounds, adding some really old guns to the mix wont help much.
The new 40mm Balkan grenade launcher could be made much more potent with a forward firing claymore type round with a rear facing laser sensor that detects laser beams for air burst rounds. Obviously the base of the round is the firing cap and propellent area , but a small sensor window facing back on the lower body of the grenade could receive detonation signals from a mounted laser to detonate the round in front of an incoming UAV and a 20 round mag for each weapon that could also be used against attacking ground troops or ATGM teams or suspected sniper positions would be a very valuable round.
For poorer countries reactivating older guns with new rounds and laser beam fuse activation systems would be useful and relatively cheap, but it would not make sense for Russia unless there was a sudden panic new problem they had no time to create a proper solution to.
The facts are that it would be much quicker to develop new ammo and new sensors for the purpose of dealing with swarm attacks in standard calibres... like 30mm, 40mm and 57mm, and 152mm as it would be to develop the same for old out of service calibres and then put them back into production and back into service.
How about super heavy flak tractors with 4 152mm high velocity flak guns each and with rapid autoloaders and proximity fuses or even cheap guidance packages they could wipe swarms of air targets relitvely cheaply from a distance of 20 kilometers or more.
You don't want to have to add new forces to your existing forces... otherwise the threat of swarm attack has made your forces less able to do what they were doing before.
A 152mm medium velocity air burst round will have a very large blast and fragment radius, but it wont be destroying hundreds of big drones in one hit... a decently planned swarm attack will come from different directions at once...
And that is another problem for the attackers... the drones themselves will need to be focussed on dealing with the air defence forces and ignore other targets because if they fail to take out the air defences they will fail.
This requires a level of intelligence and coordination that hand launched automatic drones simply cannot achieve.
A rich country like the US or Israel could probably mount a swarm attack simply by getting 200 drone teams to attack one target at one time all attacking independently but at the same time.
A rich country like the Russians defending such an attack will defeat most of the enemy threats with EW and standard air defence systems.
Systems on the way like quad loaded Pantsir SAMs and cheap ATGMs that can be used against air targets like Shturm/Ataka, or Kornet, as well as gun systems mounted on vehicles with good day and night optics and sophisticated fire control systems means they could deal with a large number of threats simultaneously, but their problem will be coordination so they aren't all shooting at one threat and the rest being ignored.
Net centricity should allow targets to be allocated to platforms to be dealt with to prevent everyone firing at the same target... and more importantly for anti aircraft forces to not fixate on the obvious threats and ignore other less obvious threats... ie a large target at medium altitude can distract you from lots of very low flying threats coming from a different direction at high speed.
If you want cheapness then you could just take an AK-130 and mount it on a large truck trailer that would alow you to fire of large caliber proximity HE shels rather rapidly but it will lack the range of a new high velocity 152mm design.
The AK-130 weighs over 100 tons and all its ammo is below decks... which modern trucks don't have.
A 2S1 has 122mm rounds and there are lots in stock... an air burst shell and decent EOs and comms systems could be used for the same purpose.