Hi Neil,
Our Docking/MDI product supports tabbed MDI and docking tool windows. Both of those mimic exactly what is in Visual Studio, and can be moved around to various locations, although tool windows are more flexible in where they can go.
Our product also has support for nesting dock sites, which means you could put a nested dock site of inner-fill tool windows within a tabbed MDI document that is in a root dock site. One of our QuickStarts shows that concept. I'm not sure if that applies to what you are trying to do.
Even if not, Docking/MDI supports all the docking window UI concepts found in Visual Studio.