I am not sure about this. 40-50 m/s can be the speed of the kites as they fly crosswind by figure-eight as shown on the website. Perhaps the speed of the wagons could be something like about 15 m/s, maybe even less.
I recall a piece of information about the speed of the KiteGen carousel which is also much lower than the speed of the kites (see the document below on the next comment), a bit (but not quite) like the speed of the tether during the reel-out phase for yo-yo systems, also compared to the speed of the crosswind kites.
In general I’m not sure that such huge infrastructures lead to economically viable solutions.