I often need to isolate some notes to listen them alone. This is not equivalent to a solo mode, because I might only want to listen to a voice, a short segment, some out-of-range notes.
If all the notes in a stave are selected, it would be the equivalent of the solo of the corresponding mixer channel.
It would work in a simple way: when notes are selected, only they will be played when clicking Play or the equivalent shortcut. This would not work if only a single note is selected, since this already means “start playback from this note”. But if at least two notes are selected, it would isolate them.