So many problems with cable-fed drones over farm-sized distances: (1) Cables rapidly exceed the vehicle weight; (2) keeping cables off the ground requires extreme tension beyond the forces capable by the drone; and (3) aerial drones are very sensitive to thrust-to-weight. You'd effectively need a swarm of drones just to lift the cable...
A swarm of drones to lift the cable is exactly what I meant: basically a cable with a set of thrust motors spliced in every n length units that can be coordinated to make the cable levitate. The total length of the cable is kind of irrelevant, it all boils down to how much cable (length and transmission capacity) you can levitate per dollar, and per watt.
