I totally agree to as it concerns the number theories. But lowering the concert pitch makes sense in some cases.

Many pieces written for voice sound now up to 100 ct higher, which matters when it goes to the upper limits of a soprano aria or if it concernes the passagio for instance. In general the orchestra sound changes to a louder sound with a different loudness distribution in the overtones when rising the concert pitch. The loudness in another problem for singers. And the sound the composer had in mind is changed too by changing the pitch.

However there might be somthing like a "natural" concert pitch. I am testing my hypothesis of a "fixed" second formant in gregorian chant. I will report as soon as I have reliable results.

Marco, I don't know what Titze second formant is. I mean the convetional second voice formant. It's bit lengthy to explain. And not all experiments are done yet. It's about harmonic formant constellations, i. e. harmonic vowels and energy efficient singing. In the attachement you'll find a scheme of all possible "economic vowels". I am on my way to compare those with gregorian chant melodies for different monastries but same texts and looking for the statitically most energy saving tuning... this, as a very short version of my new approach.

The scheme shows lines of harmonic intervals between the first and second formant. Those are the vowels of what I called "singing phonetics". For comparison Swedish speaking vowels are shown as published by Fant.

Please read Milton Mermikides' clear and thorough reflections on this subject!
http://www.miltonline.com/2014/01/07/hertz-so-good/