Ink Editor: Ok, really neat. Now "tweak" it for educators.
Make an option to default to always assuming the inking should be retained rather than the edit actually applied. This is how educators would want to use it in order to markup papers.
Also when educators are marking up a paper, they are never changing anything. So circling should default to adding an educator's comment to the paper rather than selecting -- or at least the goal of selecting is only to mark which block of text the comment applies to.
"Cleaning up" editing marks when in educator mode would also be useful. So a sloppy human circle around text should be (optionally?) automatically "cleaned up" into a nice neat tight circle around the text. A line through the text should be "cleaned up" to a nice straight line through the text, and for an added professional touch automatically add the loop at the end of the strike through which makes a "proper copy editor's deletion mark.
Finally when the paper is delivered back to the student with the editing marks and comments in place, the student should be able to start editing their paper with the ability to turn off and on the educator's marks. This is, of course, what "track changes" has supported all along. It's just a matter of making sure educator marks fall under the show/don't show logic of "track changes".