When active, only common chord progressions, or, common chords that would follow the currently selected chord type and note, are lit. Uncommon chord progressions could be lit at a different brightness, or different color altogether.
This would allow a user with no music theory knowledge to play common chord progressions and more easily write songs, in addition to experimenting with uncommon chord changes.
The problem this solves, in addition to the one listed above, would be eliminating the use of third party software like music theory apps. I've mentioned using NextChord in another thread, that is my personal use case for this feature request.
Note: maybe another toggleable feature: allow the user to select an unlit chord/note when EZ Theory mode is active, and ARP then highlights the common/rare chords for the newly selected note. Won't sound great live, but good for quick sketching and ideation workflows.