the second most awaited UI feature. not so popular, sadly. along with this wish («Possibility to select and remember different tracks and variations in patterns view») it could greatly improve workflow playing live and allow us fade out tracks without any unnecessary selections/deselections.
for now, if you have an active set of tracks to play in the performance mode, you should deactivate them all, then select the one you need, fade it with volume or filter, then select that set again, back and forth… just to fade out one track, think about the efficiency!