I guess I just don't really understand what's to gain by adding height channels to a music mix, unless it's incredibly dense music with dozens of layers (Talking Heads's Remain In Light or Yes' Close To The Edge, for example). If anything, I suspect it'll just make everything sound muddled and less discrete - it's not like they're gonna mix lead guitar in the ceiling.
Interesting quote from Elliot Scheiner regarding formats beyond 5.1:
For me, the thrill of a good discrete mix is being able to pinpoint all the instruments. It's easy enough to just "fill the room" using a stereo source and a good decoder or DSP.
ES said an interesting thing that is true of different formats over the years...and it's so true..."quadraphonic sound came too soon"....if introduced at a later time...who knows where it could have gone...it's mind blowing to me that using the equipment of that time period they were able to make such impressive recordings....hearing these recordings now on a modern format is just remarkable...