You're laying down something of an existential challenge to Head-Fi here!
(...)
But generally people don't want a house full of cables and speakers: the cliché is that it's just the wives who worry about that, but - being honest - who really wants to give up that real estate in their listening room if they could avoid it?
Furthermore, the ideal of broadcasting a good 3D image to multiple sweet spots is - as far as I know - sci-fi right now.
(...)
my hope is that the Smyth Realiser represents the highest quality available on that scale short of building a dedicated listening room.
I wouldn't say it is an existential challenge to the headphone niche. It is more like a
popularity challenge.
Please search for what professors Edgar Choueiri (xtc Bacch-dsp or bacch-sp; plus dynasonix) and Peter Otto (beamforming yarra 3d) are claiming their products offer.
If you have a limited budget and your aim is not only spatial fidelity, but also tonal fidelity, you could choose between:
A) non-isolated acoustically treated room, loudspeakers (not boutique, but pro monitors with flat frequency response measured in an anechoic chamber), xtc and room compensation DSP (or a beamforming line array...); and,
B) non-isolated and not acousticaly treated room, the faster and lower distortion headphones transducers that budget allows, an externalization DSP, a good HRTF (or PRIR) measurement.
Then I also hope, as you
hope too, that the second choice can render higher tonal fidelity for the same budget.
Caveat: current recordings may not capture the acoustic signature of the recording venue, but insert artificial reverb and level differences according to the artistic choice of the mastering engineer.
When I said that I don’t expect headphones to be as popular as loudspeakers, I didn't mean to say that headphones are not going to be popular.
Although 3d spatial accuracy of virtual speakers may marvel everybody*, I just guess that consumers seeking higher tonal fidelity are outliers. There is also what Floyd Toole described as circle of confusion that may be surmounted regarding the spatial accuracy but may continue to exist in tonal accuracy.
There is something fundamental for Smyth Research in the headphone community. There are gatherings where the product can be demonstrated and, according Smyth, that translates well into new sales.
I don't remember my grandfather. He died when I was too little. But there is a tape recording that he made at some Christmas that I like to hear. My mother also died and I wish I had recorded her with my binaural microphones. I would love to hear her voice again using an externalization device.
*I still would like to compare the spatial rendering of elevation with binaural+xtc versus third order ambisonics.