It would be great to have shared comments implemented in footnotes (a la Cornell Notes' Tufte sidenotes).
For example:
Some line of text.^[stowe: I don't like the word 'text' in this line.]
And then another user could add:
Some line of text.^[stowe: I don't like the word 'text' in this line.]^[bette: how about 'content'?]
Which might be rendered:

Already 'works' if all involved install the Cornell Notes materials for Tufte sidenotes.