I believe most of this, if not all, you can already achieve with https://hypothes.is.
For instance, the user pogotc has highlighted the text “anyone can edit” on the main English Wikipedia page. Below is a link citing that annotation (highlighting) and when any of us follow this link, we can see the main English Wikipedia page with that annotated text highlighted:
https://hyp.is/2yfMMA_CEeupaZ-oROo1ww/en.wikipedia.org/wiki/Main_Page
The annotator (highlighter) must use a bookmarklet or Browser extension, but the anybody can follow a link like the one above to just view the annotation (highlight).
But perhaps you want to be able to highlight the text but not make it so public?