Hi,

I would like to see a feature similar to Windows 7 (I'm sorry) or Gnome 3. There it is called activities. Also Cinnamon imitates that behaviour with some CinnaDock applet.

In general the feature is to have some applications in the "Window Buttons" sticky. There are still there when the application is closed, and turn into a full titled window button after the application is started.
This saves the space for an additional shortcut bar, having duplicate icons for the shortcut and later for the Window button itself.

I'm quite sure this behaviour of "activities" or "sticky applications" could be easily implemented in our "Window Buttons" as a settings check box, or just by enabling the user to select [ ]sticky on every running application  button. Additional it should be possible to drag/drop icons from the menu to the Window Buttons just like dragging to any other shortcut bar.