If you want this, I would say whats the point unless both lines are somewhat taught. If you so that you can have crosswind linear motion. Otherwise is it not just a complex yoyo design?
If you use two motors, there are conversion losses. Even just creating a static force (zero energy at zero or near zero tether speed) may incur large losses. This is why pulleys are better.
But balancing two or more tethers like this with pulleys is a bad thing because all that force+counterforce must be generated at the kite then transferred to the ground. So if you regard tether drag as a large effect, this already sounds bad.