Fletcher Munson 'Loudness Control' Video

My own familiarity with audio gear dates back to about 1970. At that point and for several decades after that, virtually all receivers (tuner, preamp, amplifier in one box) and all integrated amplifiers had loudness controls. Nothing novel about that. When the purist approach took over the high end, thanks to Harry Pearson, etc, the loudness control became a "quaint" feature that one was taught to do without, because bass, treble, and loudness controls color the sound, we were told.  Soon, they were gone from the scene. And not much missed. 

The RME Adi-2 dac has a loudness button on the remote and I use it a lot

I miss tone controls and loudness contours. I am able to modify the eq in my system via my sub volume and crossover point. It handles most situations, but am considering adding an equalizer.

I don’t miss tone controls much, but I think the loudness button might be fun to have back.

Ideally it wouldn’t be a button. It should be a potentiometer so you can adjust the amount of compensation according to the volume control setting. But maybe you were speaking euphemistically.