It's not by any means totally improbable - there's a group in Holland flying kites up to a kilometre high to generate electricity, with the intention of going even higher - up to 10Km.
Article in the Guardian:
Scientists from Delft University of Technology in the Netherlands harnessed energy from the wind by flying a 10-sq metre kite tethered to a generator, producing 10 kilowatts of power.
The experiment generated enough electricity to power 10 family homes, and the researchers have plans to test a 50kW version of their invention, called Laddermill, eventually building up to a proposed version with multiple kites that they claim could generate 100 megawatts, enough for 100,000 homes.
Wubbo Ockels, a professor of sustainable engineering and former astronaut who leads the Laddermill project, believes kites are a cheap way to harvest the enormous energy in the wind at a kilometre or more above the ground, where winds carry hundreds of times more energy than on the ground. 'We need to use all the energy supplies that are offered to us by nature, we need diversity and kites are ... intriguing and fascinating,' he said.
I'm not saying that these NOTAMS are this kind of usage, but they could be!!
SD