Great, 2.1.3 largely has this behavour, thanks!
Just some notes, middle clicking a headline only works from the headline pane and not when I middle click a LINK in the webbrowser part that displays the headlines.
And middle clicking a headline brings that new tab to the foreground, and not open it in the background as I'd expect.
Cool feature, very customisable. Perhaps an 'Open link in background tab' to the dropdown box under mouse settings