I believe it would be very handy to have separate volume control knob for master output with some slots for plugins like sonarworks speaker eq correction plugin or presonus, izotopes analizers that do not need to be exported in actual audio file. It efects only masters listening volume. Now if you insert speaker correction plugin in to masters insert slot it effects not only listening volume but also exported audio every parametre. This function is already implented in to steinbergs products and also Harrison Mixbus DAW.