Microsoft has released Visual Studio 11 Beta SDK recently after the release of VS11 Beta. It includes project templates, tools, tests, and reference assemblies that are required to build extensions for Visual Studio 11 Beta.
There is no public information regarding the enhancements and modifications to the extensibility model in VS11 Beta. It is heard that some modules(core) in Visual Studio is being rewritten using managed code and the API is also improved in the new version.
Here is the link to download Microsoft Visual Studio 11 Beta SDK – http://bit.ly/VisualStudio11SDKDownload