What happened to .....
..... the previous Airbus experiment to use wind for the same thing?
Did they decide the Flettner rotors was a better solution? The issue I can see with the rotors is that they produce thrust at right angles to the wind direction only. So for crossing the Atlantic (East-West or West-East) they would make best use of winds coming from the North or South.
Kites can be flown within the available wind window (according to the wind direction) and can provide thrust at an angle either side of the wind direction.
I would have thought that the two technologies could be fitted. Into a head wind neither would be of use, in a cross wind both could be used, and in a tail wind the kite could be used.
By choosing your route to maximise trailing winds you should be able to get the most out of both technologies.