This is the formal request for a row marker that shows when a note is still being processed, or more precisely, has not been Note-Offed. This indicator would fill the note field (column 1 of each channel) and simply be a thick vertical line between a note on (such as C-5) and a note stop (like == ). This will remind the user that a channel may still be outputting signal.

Initially this could be made to be a graphics-only function, in which the row is checked for a previous note (even from a previous pattern) and, if a proper note is found, a toggle indicates that continuing rows should be drawn with this indicator until a note stop switches the toggle back. The function would simply paint a bitmapped line instead of the usual dots. Future versions of this feature will detect if a channel's audio signal has stopped and the toggle can be turned off so the rows are drawn with a different indicator (note on but audio off).
With this feature should be an general preference so that it can be optioned off by the user.