It would be helpful to have an option to record microphones in separate channels from the main mix. That way, the balance between the microphones and the music could be adjusted in a DAW before publishing the recording of a mix. This could be used to record crowd noise during a live mix by selecting the direct monitoring option for microphones but not actually setting up direct monitoring on the sound card. Such a setup would make postprocessing easy because the crowd noise and music would already be perfectly aligned in time. Compared to using a field recorder like described in http://djtechtools.com/2017/12/11/record-mix-dj-set-live-crowd-noise/ this would avoid unnecessary digital-to-analog and analog-to-digital conversion so it would preserve the sound quality of the music. Doing this currently would require sending the output of Mixxx to a DAW while the DAW records the mics separately. It would be nice to only need Mixxx running during the performance for this.
Would you also want to add noise-canceling to the mic processing channel to remove spillover from the main/monitor mix?