In-line commenting.
Invisible by default so they don’t distract, but you can easily switch visibility.
So the reader particularly interested in some section could dive into the comments particularly about that section.
Also, as a further feature, you could color code different comment types, like:
blue (default): just a comment
yellow: fix suggestion
brown: link to previous discussion / relevant resources
red: critique ?
Also see @Emrik’s comment with more rationale.
Expose “voting tribes” in the comments.
We could run a similar algorithm to X’s Community Notes. Then, on contentious topics, we could easily see the main axis of disagreement. We could also have a comment sorting option, that upranks those upvoted by people from both sides of the disagreement.
See this thread for discussion and corresponding post for algorithm description.