Thank you for your restless coding !
Yesterday I had a dream about this plugin, 'was going to recall this idea today
btw. two other ideas:
A) a Fletcher Munson EQ plugin. It has three sliders: 1st one to let the user input current SPL, 2nd one to change volume while auto-compensating for the F-M curve, 3d one to over/underemphasize the EQ curve. It would be best if it used linear filters.
One of possible usages: mixing over the noise floor of your room, while setting levels as you were mixing at lower levels.
On a second thought. In an advanced version it would be a dynamic equalizer...
B) a very connected idea is a Fletcher-Munson compensated, *resynthesis* based compressor acting as a "volume knob of war", precisely scaling each and every single frequency (offline, but it's no problem). Great for correcting mixes that are undercompressed.