Why is holophony uncommon?
 

The few holophonic recordings I have heard sound great. Why hasn't it taken off?

Price and need.

The price point is an obvious deterrent for pro-sumers. The small "egg" isn't out just yet, but it's still pretty pricey.

Regarding need, I can mix 5.1 in post for narrative works using foley from sound effects libraries. I don't necessarily want the real sound from the set. I just need clean dialog - and I might even ADR that.

Holophony is really best for live events and natural documentaries. In both cases you want to be truthful about the environment. Getting a surround crowd at a football game or awards show with a single mic stand is really nice, logistically - though you still need to mix in the announcers, interviews, on field noises and music bumpers. A single holophone in a rainforest documentary would also be a nice solution - though, again, you will probably want additional mics for dialog and interviews.

The other place where it would be useful is to sell consumer HD cameras with a built-in surround audio feature. Of course, this needs to be much cheaper, with low-cost trumping performance.

because holophonic recording is a hell to setup (several mics, all correctly phased, needs multitrack recorder) and it does play well only on headphones.
do not mix holophonic recordings with binaural recordings, the goal is the same, the technique is different.
5.1 is way easier to give a surround effect and is supported by most players.

I'm not sure of the original poster's intent, but I was thinking of the Holophone. http://holophone.com/ This removes the need for multiple mics and phase control. For the DTS encoded version, you can record it to a stereo pair.

I'm familiar with binaural recording. Is there a more general meaning of holophonic? If so, what are the details?

Thanks!

The other possible use for that mic is for plain stereo recordings, in theory you can steer the image similar to the Soundfield mic