The idea of Thethered UAVs isn't new. Problem is probably the danger of high voltage tethers that they use.

Why do they need a high voltage tether? They don't need a high voltage battery.

To transmit power, its better to use high voltage and low current. Reduces transmission losses; uses much lighter cables. Then where the power is needed its stepped down with transformers or 'buck converters'.

Thanks, those were the trigger words to conjure up an interesting Google results page.

If you need to connect them with a wire, you might as well sustain them in the air with a long stick and spare the energy.

Might still be cheaper (storage, transport, setup, investment) than a crane or scaffolding when you don't need to support heavy loads. And scaling would only be limited by how much power you can push through the chain, whereas sticks need to be quite massive just to support themselves once you go beyond a few meters of length.

It's not a swarm, but I think the one drone from 3D Robotics can be tethered for essentially unlimited flight time. So that's some progress towards what you have in mind.