Peter Provost has started a petition to include unit testing support in all versions of Visual Studio 2005. While I agree that unit testing should be essential part of all development, I don't think Visual Studio is the place to introduce an important new API. I think a much more fitting place would be the BCL and SSCLI/Rotor. At the moment the BCL has an extensive set of unit tests. I would be in favor of converting these over to using a core testing framework (say 'System.Testing'). We would then have a standard API for writing tests under all implementations of the CLI. I think this is where real value would come.
Having said that, there is going to be a need for unit testing support in standard versions of Visual Studio 2005. At the moment I am developing a testing tool what will work in all versions of Visual Studio and integrate with Visual Studio Team System. It will support NUnit, csUnit, MbUnit and the testing framework that comes with VSTS. The idea is to allow those using VSTS to run their existing unit tests unchanged vier the Team System extensibility hooks. It will also allow those not using Team System to run tests written using the Microsoft testing framework.
So long as Team System remains a premium feature of Visual Studio, there is a point carrying on with this and other projects. I am relieved that Microsoft have chosen to tread relatively lightly on the thriving .NET tools community. I think this can only help encourage innovation and cross fertilization.