It might be worth noting that you don't need MSBuild to invoke the Content Pipeline. MSBuild coordinates the build, and from the point of view of a VS project, we need it. However, if you are building your own tool or editor, you can very easily not use MSBuild at all.
It is perhaps easier to think about how it works, and to configure your content builds using MSBuild, but you can bypass it altogether if you like.
The point I'm trying to make is that the most important missing piece is the Content Pipeline, not MSBuild. Not that it helps at all to know that... :-(