DW observes "The jetstream wiggles around a lot, by many hundreds of miles. I
don't
see a tethered turbine in one location being in it more than a small
fraction of the time."
Not only that, a kite tethered on a 35,000 foot string would allow the kite
to move around enough to make flying near it hazardous. These things could
only
be approved well away from commercial air corridors.