Indeed. The ability to click on an interval and immediately hear it -- and/or simultaneously see it played on the piano -- would be quite nice. (Or, conversely, the ability to see piano notes instantly rendered on a staff and have the intervals identified.) Combining two learning pathways -- visual and aural = win.
I largely ran out of time to extend/improve it several years back, but it still gets quite a lot of use; students of subscribing teachers can use MIDI keyboards as well, which makes the instrument/theory link quite tangible.
