As i answered this question How do I reverse engineer a chord progression from a melody? - #2 by Alexxxis i thought that HP actually should be able to do that itself.
A Harmonize/Reharmonize Button which fills chords in selected measures which fit the melody already entered above. With two additional Simpler, Complexer Buttons to suggest more simple triads or more complex, borrowed, extended chords.
The opposite of 1. A Melody Suggestion Button filling notes over a progression. With two additional More, Less Density Buttons to generate more or less notes.
I guess it is sufficient to add 4 extra buttons which can be grouped in the menu. Both is technically not so difficult to implement as it sounds.
In 1 Chords are chosen from the Key. Those chords which contain the notes entered above are preferred. (similar to Guide function)
In 2 the notes are chosen from the Key Scale with a higher probability to match the chord notes (see Guide function) especially if the notes are longer. Usually melodies use a 1/8 resolution with some 1/16 (those more with low BPM´s)
Each press on one of the four buttons should regenerate new content in the selected measures.