Just watched this. Apparently it was funded by the European Union.
I can't see any benefit from it, and dozens of issues.
Primarily, the cost of building what amounts to an enlarged and reinforced Nascar circuit and being able to land on it in reduced visibility.
In fact, landing safely on it under ideal conditions could prove deadly.
He says it would eliminate issues with crosswind landings, but the angle an aircraft was taking relative to the wind would constantly be changing (due to the curve) and the wind direction at the beginning of a take off would be different when rotating and climbing out - unless the diameter of the circle was absolutely enormous, but then an airport would consume hundreds of sq km.