This may have been requested in other posts. If so please forgive the redundancy.
Custom notes assigned to keys. You select “custom keys,” and enter an edit mode, like chord edit. You click the notes from the keyboard or fret board to assign them to keys. If limited to White keys that would be fine. If it notes could be assigned chromatically that would great. Once editing is finished the selected notes become the notes the keys sound. I’m not sure if this hypothetical “custom scale” would be locked to the chord or handled some other way.
I can see many benefits to this. One interesting one is re-entrant tuning patterns like on the ukulele and other instruments.