There is science to be gleaned from all of this, but I think that it is far to complicated for any company to solve in the short term, and what we are left with is generalities. I agree that the science of it ought to be nailed down as far as possible, but also understand that there are too many variables for any definitive answer.
If you rented a hall, seated the instrument-players in their normal locations on stage, hung a microphone over the conductor, recorded every note on every instrument at lots of different dynamic levels, and if you never touched your gain faders throughout this process, and you never changed the volume of the samples, you'd get Natural Volume; and to use such a hypothetical library, you'd never alter CC7 or CC11, you'd just use velocity or CC1, and it would control timbre and loudness at the same time, always keeping them in their natural relation.
This hypothetical library would be inferior to VSL in lots of ways, but at least it serves as a model of Natural Volume made easy for the end-user. Beethoven had to decide among ppp .. fff for each note but that's just a simple one-dimensional variable for dynamics. I have to set velocity, CC7, CC11, DynR, Velocity Curve, and probably some other variables I'm overlooking. That degree of control -- 5 independent variables -- is nice when I want to make unnatural sounds, but it only gets in the way when I'm trying to do things like Beethoven did them.