This vould mean that the power coefficient (Cp) is doubled for a wind turbine because it would use two counter-rotating rotors instead of a single rotor of same swept area. So the measured power coefficient Cp of 0.35 would be 0.7, so above Betz limit (0.593). It is not possible. At the best, counter-rotating rotors for a turbine could marginally improve the Cp, and at the price of higher weight, cost and complexity.
One more detail: since each of the two rotors turns in the opposite direction, a rope-drive transmission would need to be installed for each of the two rotors.
Kitewinder uses a simple turbine (with only one rotor), and the system does not rotate around the tether axis.
Perhaps the reason is that the (essential) right angle between the hub and the pulley (and the belt connecting them) allows to neutralize the torque (among other useful advantages including simply a correct transmission) by the traction force, a little in the manner of a helicopter tail rotor. Moreover, a sort of weather vane is used, allowing the turbine to be settled in the wind direction.
Conclusion: Kitewinder made a great job on Kiwee, that it is difficult to improve, but easier to make worse.