I like this idea. Currently you can, of course, add a comment and quote the relevant text in your comment, which is a standard method on forums. (In QDL, select the text you want to quote, and then click the "Add Sub-page" option in the Action Menu, and the selected text will appear in the editing box.) But what you're talking about would mean that when reading an article, you'd see what has spawned comments — when you're reading the article. ;) So you wouldn't have to read the article, and then read all of the comments, and go back and figure out what it all means. You'd see that there is a footnote, and if this is a section that interests you, you might want to read the footnote.

For that matter, it would be cool if the text of the comment appeared in a on-mouse-hover pop-up. I normally stay away from these, as they get overused, and too many pop-ups can make mousing over a page feel like walking through a mine field. Maybe it should be a user option (in the global Settings) as to whether to display inserted comments as pop-ups, or as footnotes. Another approach would be to make the "inserted comment" designation a click link that would split the paragraph, and show the full comment right there.

There isn't any way of detecting where in the document a user clicked, but there is a way of detecting a selecting. So instead of clicking in the document and then clicking a button, the user would select some text and click a button. Then the note marker would be inserted at the end of the selected text.

I'm thinking that the footnote designation would be an asterisk, with a number beside it for which one it was. For example, *¹ would be the first footnote, and *² would be the second.