I get the point. I just value a good measurement system that is based on the most recent science more than an older system which is maybe not at eye level technically but comes with a somewhat established (p)reference curve.
If you look around in the community you will notice that the subjective agreement on the Harman Headphone curve is still a bit controversial. And it is not just a lot of (end) users who prefer subjective modifications. Also the engineers who make such measurements do often publish their own tagets. Some of them are only slight balance changes around the Harman curve. And some of them do promote their own idea of "neutrality" which comes with much less bass and a different weighting of mids and treble.
All of that does not mean that the target itself is fundamentally wrong and has no scientific foundation.
Still, the practical variance we see out there - which is due to individual ear geometry, taste, circle of confusion and all the other factors that have been thoroughly discussed before - is enough for me to doubt that the approach of a specific singular curve is stable enough (yet) to qualify as a common standard for both the average and especially the hi-fi community. This situation can be proved by the very simple observation that nearly every thread that shares FR graphs together with the Harman curve as a reference is - at least temporarily - subject to fundamental debates about perceived neutrality and the validity of Harman. Just searched a few threads for the buzzword "harman": HD800S review: 5 of 29 pages; HD650 review: 4 of 15 pages; Focal Clear Review: 3 of 25 pages.
Maybe some people expect the works of Harman to break the circle of confusion and arbitrariness of taste some day. Personally, I do not think that this is going to happen. At least not to the extent that it solves all the essential problems. Just consider the retrospective of music productions or the practical arbitrariness of most speaker/room responses. You cannot fix the reality by just claiming a specific curve to be the reference!
All this arbitrariness leads me to the conlcusion that we are not quite there with the approach of a singular (Harman) target, yet, and that we need better technology and more reasearch to improve in our field. And I think that the 5128 HATS might be a good choice to get at least one step closer to a next generation of headphone measurement. Remaining in an established ecosystem may be practical thing, but it is a technical limit after all.
Regards
Dreyfus