There are two existing requests that are more specific than this one as it is presented now:
- Introduce chords as musical units (a feature reviewed)
- Select / highlight the scale to work with on the piano roll (currently a draft)
For the sake of modularity 
between requests, it would be useful if you could look at these two requests and see what else not covered there should be covered here. Needless to say, you can also provide feedback on these other features.