Looking at the beatiful show, I cannot avoid thinking: "each of them a potential weapon".
So in fair weather, when communication is smooth and all navigation systems are working, it's entirely feasible to coordinate a swarm of 10 000. Wow. :)
Soon enough, they will be coordinating each other in the presence of electronic warfare, and swarms of 100+ fly already, so 1000 is the next step. Anyone doing air defense is probably designing energy weapons (lasers, masers, etc) at a pace approaching madness, besides making ever-cheaper drones.
As for the environmental footprint - if each drone withstands 10 performances, they will probably save resources. :)