Lack of concern
Forget your .."how will we make it light enough" ... or ... "how do you pass lots of volts through a thin enough cable" ...
Is it just me that thinks 10,000' ~ 15,000' of "tether" may pose a slight hazard to anyone wanting to use the skies ???? Visions of wartime London and the sky full of barrage balloons springs immediately to mind !!
Durrr !!!!