I am sure there is a threshold where two kites beats on single large kite.
I have seen people trying to fly inflatable 17s and it seems like the added surface area only stunts the the basic performance of the kite to the point where any boost in performance is pointless.
I agree with Windstoked, this concept completely opens the door for improved kite performance.
Windstoked is definitely on to something, have an inflatable at the top of the pack probably would eliminate the floating requirements of the latter dogs. Air cells could be flown below. Ram airs are typically 2x as efficient with a properly filled foil, so that boils down to half the drag! We have not even begun to talk about the weight reductions yet either.
Furthermore this might be the key to advanced depowering, I am sure it would be possible to sheath any of the non-primary kites.
Assuming you could re-sheath after lift off, launching could potentially be easier as well because launching a 7 m2 inflatable (+5 re-sheath for an effective 12) is an easier task than a 12.
Before anybody starts talking about wind level conditional variance, I would say putting the foils right next to their effective boundary layers, gets maximum performance of each foil without neighboring disruption while keeping the kites close enough to be in the same effective free stream flow. (Notice in the video the rig had issues with the kites flying independently at certain times)
You could probably get a grant to do research on this to if the end product boosts performance on power generating equipment.