After text is selected in preview mode popup nice simple context menu add add there icon for highlighting. After selected, preview mode view is updated and we can see new highlight
Plugin which list all highlights in article in right ribbon bar. Similar like search results, but only get highlighted text
If clicked on hashtag the same ribbon in right will show all highlights from the notes with same hashtag.
An embedded search can handle 2 and be modified to handle 3.
The previews will show some extra text around the highlights, but the highlights will be highlighted within that.