Two features that would be useful for me:
1. Being able to see multiple chords in a time sequence that use a given note, say E4. My teacher told me that I should practice singing a given note while playing multiple chords having that note. This would help with singing, ear training to recognize chords by the ear, as well as learning chord progressions for a given song. Initially I would like this to be any chords through a given note, whether on the scale or not, and later also limiting to those falling on a given scale.
2. It may be helpful to be able to rotate and flip the fretboard diagram. This is just to match the orientation I see elsewhere like in a book.