Naysawn has announced that the Visual Studio unit testing framework (MSTest) is moving into the Pro SKU of Visual Studio. That's a good start, but I want to lobby for going the whole way:
Please move the unit testing framework into the .NET framework.
Just like MSBuild, this is a key bit of technology. (What I'm talking about here is, at a minimum, the libraries and the console runner.) Requiring an installation of Visual Studio on an automated build machine is a non-starter for a lot of teams. I suspect that much of the resistance to move away from NUnit and friends will disappear when we can build and run tests without needing Visual Studio at all.