Highlight parts of a post that have been quoted in a reply

I’m very interested in a highlighting feature à la medium, though more basic. Could you clarify whether the team has any interest in adding any of the following features into core (whether as PR or from the team itself) and if not, whether you’d be willing to support a plugin in core should it be required:

  1. Adding a “Highlight” button next to the “Quote” button. Pressing this button would add a very light yellow background to the selected text. Every time another user presses the button for the same text, the yellow background becomes a bit more saturated.
  2. Making it so the pressing the quote button also does what the highlight button does (in addition to its core function).
  3. Adding “Highlights” as a tab to user activities, listing links to all posts a user highlighted
  4. Adding a user setting that hides all highlights by other users (this could probably be done via a custom theme, if the necessary classes are provided in #1 above)
  5. Making it so that clicking into a highlighted text gives you a popup listing the avatars of all users who highlighted that text segment.
  6. Add an admin settng that disallows highlighting on a per topic and per category basis. (Or, perhaps better, which hides other users’ highlights permanently while still allowing users tho add highlights for themselves.)

I would not want to notify anyone about highlights and neither should highlighting count as a revision of the post. Any logged in user can highlight anything.