Mostly I was thinking of my own use, where I have a classic text that I don’t want to “pollute” by inserting macros, transclusions, etc. But annotating HTML, where editing the source can be extremely difficult, is a good use too.
I could add a “footnote” to the bottom, that would collect the annotations.
This, if possible, would require that the dyannotate widget insert named anchors. That’s the only way I know to navigate within a tiddler. Perhaps @jeremyruston could comment on the feasibility of that enhancement.