Working with MSBuild files can be a pain sometimes. Sure, you can open them in Visual Studio and get partial IntelliSense and color coding, but a Visual Studio integrated visual designer to help put them together would be much nicer.
The designer will consist of a multi-tabbed editor window. The tabs would consist of an XML view, and a graphical view. The XML view would use the standard Visual Studio XML document editor. The graphical view would implement the IDesigner interface to provide a Windows Workflow-like graphical view of MSBuild files complete with target dependencies and tasks.