This state tracker called "nine" is not merged to Mesa master, at least not yet, but can be found in the ~jsindholt/mesa repository.
The state tracker's documentation describes this Direct3D 9.0 ST as providing:
What is this?
An implementation of the C++ API as seen in Direct3D 9.0c. It's meant to be an easy and reliable way for WINE to emulate D3D9 applications from Windows on free platforms (though I believe the WINE devs don't give two shits about it), and enable users to more easily port their Direct3D 9 applications.
What is this not?
A binary compatible, or COM compatible implementation of Direct3D. It is not meant to run on Windows, nor does it expose the regular COM interface. If a COM implementation is provided, this matter can of course be discussed.
Well, there you have it. Let's see if it ends up being used by Wine or any other free software projects. This is just the latest Gallium3D State Tracker after there are already some for OpenGL ES, OpenVG, EGL, OpenGL, OpenCL, and others are still emerging. We just need the Gallium3D hardware drivers to catch up so Linux desktop users can start taking advantage of such support.