Make plain text version of embedded notes available via the API or by default
When you highlight part of the document and add an annotation, create a plain text version of the highlighted part of the document that can either be retrieved via the API or accessed by the user by default. The user could opt to access the plain text version by clicking "read transcript" (or something of the like) on the embedded note.
This would help with readability on mobile devices. It would also probably help to give editors the ability to correct the plain text version in case it's not totally accurate.