I like the thought of removing drones. I find it hard to believe that 500+ players aren't enough people to man a sufficiently-sized bomber force to get the job done after a rebalancing of side assignments. As for the argument that bombers are too vulnerable without drones, FSO IS supposed to be a TEAM event, right? 500 players operating as squadrons, not gaggles? If a squad flying bombers doesn't stay together IMO that's their decision and they SHOULD face the consequences.
Another option is this:
Each squadron assigned to fly a bomber is given a maximum number of aircraft they can utilize. Say, a 7-10 squadron can field a maximum of 12 bombers, to coincide with their +2 allowance. The squadron has 6 pilots actually show up. They would be allowed to have three guys launch with formations to fill in their numbers. If 11 guys show up they can either have 11 players launch in singles or use whatever combination of drones, singles and gunners they need to match their 12 bombers allowed. Combine this with--instead of the "Credible Force" requirement based on how many times over the target can be leveled--assigning each target a "number and size of squad" requirement like some special objectives have in past setups (say, a small airfield must be attacked by 2 4-6 squadrons or 1 7-10 squadron, or something along those lines)