We quietly shipped the Visual Studio Integrated and Isolated Shells when Visual Studio 2010 Beta 1 was released.
The shells are still work in progress as we made some changes since VS 2008 SP1. Both shells will have all the new goodness that came with VS 2010 including the WPF UI and feature updates to the web components, a brand new MEF based Editor, along with xcopy pkgdef support. Another big change was we moved the shell setup to use the same setup engine as the main VS product.
You can download and try out the shells from here:
Integrated Shell: http://www.microsoft.com/downloads/details.aspx?FamilyID=ee907896-e8f4-4378-9405-2593ddb38376&displaylang=en
Isolated Shell: http://www.microsoft.com/downloads/details.aspx?FamilyID=308b82aa-39f9-456e-b6d7-5d348b6f7015&displaylang=en
To create extensions that work on the shell, you'll need to also get the Visual Studio 2010. (http://go.microsoft.com/fwlink/?LinkId=147422)
You'll also notice the Shells are a lot bigger than what we shipped in Visual Studio 2008 Service Pack 1. We're carrying both the 3.5 and 4.0 .NET Framework redist packages inside the shells at this time. This will be fixed in Beta 2 as we remove those and replace them with the small web download for the Frameworks which will reduce the shell redist sizes back to the Visual Studio 2008 SP1 levels (120-150 MB).