We've already talked about the usefulness of a 'select special'. Let me highlight a particularly useful capability: 'Select note'. I often manually select every root or 5th or 6th or whatever in a diagram, to adjust them en masse. It would save time and avoid errors if I could say "select every sixth tone" in this diagram or on this page.

Ideally, I would also have "select-add" and "select-subtract" options (i.e. "add to selection" and "remove from selection").

To explain, I am often working with large 7-8-string fretboards (15-19 frets) with full arpeggios drawn out in light grey, on which I flag certain notes of interest. So on any given diagram, I might have ten-fifteen occurrences of the same tone.