There are efforts to implement Direct3D 10 in Wine. A Google Summer of Code project is ongoing to start the development, Andras Kovacs is currently writing a stub DLL. I am mentoring his work, but more as a Wine hacker than a CodeWeavers employee.
We do not have a timeframe for a d3d10 implementation yet. The thing is, it is not dreadfully important right now, and there is more demand for d3d9 improvements. It will be some time until games are d3d10-exclusive. But I won't say that there will be no d3d10 implementation in 6 months. It isn't impossible to get it by then, but I can't promise it either.
A major factor is OpenGL 3.0, which is very simmilar to d3d10. Currently we are waiting for the final OpenGL 3.0 interface, and then MacOS and Linux will have to support it. I am confident that we will see GL 3.0 support on the Nvidia Linux very soon, but I am less confident about MacOS or Ati. MacOS' GLSL implementation is still rather buggy at the moment, so MacOS is somewhat stuck to D3D 8.1-Level features. Hardly any games really use 9.0 yet, EVE Online uses DirectX 7-Level features for example. So the question is when GL 3.0 support will be around.
Also note that you will need a D3D10-Capable graphics hardware. We can't do wonders and run D3D10 on older hardware, at least not at usable framerates.