I like the pin button on the left sidebar, but once you've pinned it, there is no way to unpin it unless you go into Panels Configuration and switch it back to auto-hide. Maybe the icon could stay there, and be converted to an "unpin" button that would put it back in auto-open mode?
If you did something like this for the right sidebar, too, it would completely replace the functionality of the open/close buttons in the status bar.