What in your opinion is the ideal (in terms of listener preference) frequency response and directional characteristics for a loudspeaker?
It's an indisputable fact that the Harman data was collected in a scientific manner (evidence-based) but I don't see how "average listener preference" relates to accurate reproduction of the recorded signal. In my view it merely provides information regarding people's tastes.
Regarding frequency response, most people don't listen to recordings of acoustic music and some have never listened to a single live unamplified concert in their life; "realism" is not a requirement for the majority. Besides it is impossible to determine "realism" unless one is familiar with live and uses long term listening assessment and adequate recordings. An short-duration AB comparison is totally unfit for such purpose.
I listen mostly to classical music plus a bit of jazz, not to Krell-Barbie-Pigeon-Bubbles nor pop nor techno, and don't care much about "air" around the instruments (exaggerated top octave?) nor the "soundstage" effects (wide dispersion?) nor "dry, fast" bass (dip in the upper-bass?) nor "enhanced" detail (mid-woofer breakup resonance?).
I'm sure that the BBC sound engineers were far more well equipped to determine what was/is the "correct" or "neutral" balance at the listening spot. Not only because they dealt with live and recorded sound on a daily basis but also because unlike speaker manufacturers they were able to compare the sound coming out of the speakers with the real thing (the BBC runs a number of ensembles including large choirs and symphony orchestras and broadcasts classical as well as other types of music).
As for directional characteristics, again I think it's easy to again make a case regarding the different requirements of distinct music genres.
Good recordings of unamplified music played in naturally reverberant venues allow the listener to be drawn into the original soundscape. Listening room boundary reflections will have a negative effect, interfering of even destroying the illusion of attending a musical event.
Studio produced music on the other hand may sometimes benefit from boundary reflections. Such recordings constist on a collage of mono tracks that close-mic'ed in a semi-anechoic space(s) and then manipulated to create the music. They sometimes sound "dry" and "uninvolving" and they're hardly ever meant to sound realistic.
Besides the boundaries of most domestic listening rooms are untreated and not always symmetrical. Side-wall reflections in smaller European or Asian sitting rooms will have significantly more impact than in the plentyful space in lounges of North American homes.