This is disingenuous, it completely burries the functionality. I also wonder how this would alter the topic view, as right now you can click the star in the title and get the current topic starred.
Compare this to GMail: when they added the “Important” marker, they added it back, front and center; each time it can be clicked to toggle the state. They even added a “Mark as (not) important” in the “e-mail thread actions” menu so that it would be more discoverable.
With this new design, it seems you would need to click the topic (and read some posts if there are any new unread ones because AFAICT you can’t go straight to #1 from the topic list), use the post counter to go to “Top” and bookmark that first post. This does make it feel like jumping through hoops…