I'd love to see additional visualization options for anchored notes and potentially anything else that has a Bible reference association. Wide margin is one possibility. You could potentially achieve this by adding a "Notes" section to the Insights panel. It would be great if the Insights panel could be configured similar to custom guides (turning things on / off), and it should save as state for any custom layout as well. This would allow a strict personal notes view as a wide margin, for example.
I'd also love to see an "inline notes" feature. Here's an example of that in the NIV+ bible app:
It would be great if I could actually select a set of resources / notes I wanted inline like this!