I discuss what I call "LSESL", or Line Source ESL design, in my most recent article at Dagogo.com. I'm referring in that term to the Kingsound King, a large planar (You can tell I'm just a BIT excited about this technology). Quad has used a similar concept in their speakers for years, and we all know how that's been received. To my ear, the multi-driver concept with the ESL technology is a fantastic combo. One can certainly achieve a tremendously satisfying result implementing multiple ESL drivers as opposed to cones.
Why so few high end line arrays?
To me the intrinsic "wall of sound" of this design are compelling. I recently tried a very nice 3 way w/ stereo subs in my system after 2 years of line array-only listening and the lost impact and scale of eight midbasses/ribbons per side was profound. I was immediately aware of the music emerging from boxes, despite very nice imaging. And it's not that the arrays exaggerate the size of voices and instruments. Does the materials cost dissuade manufacturers? Is it the size? Seems like relatively unexplored territory in high end home audio.