Fair. I once was told by a senior NREL engineer that industrialization of a different concept than HAWTs would take over $1B in investment. Which is a lot in a low-margin, capital -intensive business like wind energy. And that number is probably on the low end.

Kites have the potential of much lower material costs to produce energy. If you have a pumping cycle kite, the "support structure" is the tether, compared to the tower and foundation required for a HAWT. The problems are indeed well known: 1. Tether material difficulties. 2. Need for self-launching 3. Airspace sharing problems at heights of kites 4. Controller design. This last one is what intrigues me personally.

The paper looks at vertical turbine arrangements, but the linked article about the paper starts with "The research suggests that the now-familiar sight of traditional propeller wind turbines may be eventually replaced by the sight of wind farms containing more compact and efficient vertical turbines." I had to respond to this rather wishful statement.