1. Microsoft untangles Direct3D from Windows, and publishes all the APIs for it, allowing Direct3D to be implemented natively on other platforms - if SGI, Sun, HP and 3D Labs (remember them?) can do it for OpenGL, I'm sure Microsoft can do it for Direct3D. In fact they could do it for the whole DirectX suite, but I'll take the graphics for now. This would then allow the likes of nVidia to ship both OpenGL and Direct3D implementations with their driver packages.
The d3d9.dll in WINE could then call down directly to the native D3D9 implementation and pass the data structures directly. I think this'd be about as thin as WINE could get. Or nVidia actually supply a d3d9.dll that does the job directly - installing it into the WINE file structure could be tricky though.