Employee Daniel Moth added: "DirectX 11.1 is part of Windows 8, just like DirectX 11 was part of Windows 7. DirectX 11 was made available for Vista...but at this point there is no plan for DirectX 11.1 to be made available on Windows 7."
That being said, 11.1 does not add any killer features, with the exception of stereoscopic 3D, which has yet to be widely adopted.
The full update list:
Shader tracing and compiler enhancements
Direct3D device sharing
Check support of new Direct3D 11.1 features and formats
Use HLSL minimum precision
Specify user clip planes in HLSL on feature level 9 and higher
Create larger constant buffers than a shader can access
Use logical operations in a render target
Force the sample count to create a rasterizer state
Process video resources with shaders
Extended support for shared Texture2D resources
Change subresources with new copy options
Discard resources and resource views
Support a larger number of UAVs
Bind a subrange of a constant buffer to a shader
Retrieve the subrange of a constant buffer that is bound to a shader
Clear all or part of a resource view
Map SRVs of dynamic buffers with NO_OVERWRITE
Use UAVs at every pipeline stage
Extended support for WARP devices
Use Direct3D in Session 0 processes