Attacking this problem from a different angle might shed light on why these things aren't flying yet.
5 years ago, the wholesale rate for electricity was about $30/MW-hour.
If an Flying electric generator were able to get aloft a 1 MW version and maintain 60% availability, it would generate about $160,000 / year.
Considering these are actually, little more than helicopters, the economics of helicopters probably still apply. You do need to pay the mechanic to maintain them, and helicopters need a lot of maintenance.
I suspect that the reason these aren't flying over every available piece of jetstream is that it is not economical to do so. It has the appearance of being free, but the realities bite them in the rear.
One of the proposed projects is 45000 lbs.
So would it be wrong of me to suggest that the amount of current you need to send to the helicopter to get it airborne is 4 times what you could expect getting back from it, when the motors turn into generators.
I remember seeing a transformer for a 700 MW power plant. It was the spare. It was the size of a small house and took Three Phase 480 V up to 48,000V. I also remember friends making shocking devices that turned a 9V battery into 14,000 V which they would hang on doors.
Can you make a transformer for a 1 MW generator light enough to step up the generator current on the generation side and step in down on the motor side of the equation to fit on the helicopter/generator.