This looks great. Just a couple of comments:
- I found a bit strange that article-related actions such as watch and discussion are initially present at the toolbar and the button ribbon. I would expect them to be added to the toolbar once the ribbon is no longer visible but not initially (when the toolbar looks not article-specific).
- As Steven mentioned, it would be great to think on ideas for using the more prominent search. That goes beyond the current project, but a more prominent search enables new exploration possibilities we may want to consider: It would be great to show richer suggestions, and start showing related information just when you click on the search bar (even before typing). Initial search suggestions can be contextual to the section where you are.
Pau