+1 for modular approach of all parts of GUI.

Robert, while this is not exactly what you proposed, but I think is a more universal approach and should work for most what you are after:

All tabs dockable & un-dockable - floating. User defines which buttons to display in the tab of specific category or even if to display a certain tab at all. Add "Action" tab where user can make any buttons they want based on any existing shortcuts. Ability to save layout as "default" for multi screen setups.