I have recently been playing around with Sound Variations and came upon a set for Spitfire's BBC SO Core library. The set includes the high and low notes as sound variations, sometimes dependent upon articulation, so they appear nicely highlighted in the piano roll. But there is a caveat: it appears that you cannot play these notes. This isn't as much an issue when there is just one high and one low, but if you take a string instrument that has harmonics or a wind instrument with flutter tongue, the playable range is altered. The high and low note for the articular is also specified. If that note occurs within the normal playable range, that note does not play a sound and you must remove the sound variation.
Thus, I came to realize it would actually be rather spectacular if you could specify the playable range of the instrument as a whole within the sound variation config and then have the option to override that based on the active sound variation. This could then highlight the keyboard in the piano roll (or alternatively, dim the keyboard outside of the playable range) so you see, at a glance, what can and cannot be played on your instrument.