I think the main advantage to updating The Witcher 2 for DirectX 11 would probably be performance, not necessarily improved visuals.
CD Projeckt stated in an interview that they stuck with DirectX 9 since they made a list of all the features they wanted in their rendering engine, and that version of DirectX was sufficient. And I'm seeing plenty of modern effects such as Godrays, SSAO, Bokeh Simulation, HDR, what looks like subsurface scattering and parallax mapping etc. Plenty of the latest rendering techniques and buzzwords.
The performance improvements could be substantial though, since DirectCompute can be used to speed up SSAO, Bokeh Simulation (I think that's call "cinematic depth of field" here), and physics calculations. Geometry instancing could be of some use too, no doubt. Though not much, from what I've seen.
As for the famed DirectX 11 tesselation, I have yet to spot any places in the game where that would bring a significant improvement to the visuals.
So basically, I would also love to see a DirectX 11 patch in the future, but I wouldn't count on it since it would require a tremendous amount of work to do properly, and would probably have minimal impact on the look of the game,
Post edited May 17, 2011 by xenobrain