A lot of the work is already done: http://bugs.winehq.org/attachment.cgi?id=22871. There's a stub dxdiag.exe already in wine, and last year some students from UCLA coded a relatively functional dxdiag.exe. It's not yet in wine, though.
I don't think it would take a GSOC amount of work to get it cleaned up and into wine, but I may be overestimating the quality of the code. Regardless, I'm sure others have more to say.
-- -Austin
I noticed that much of the work was done. I did indeed plan to use this as a reference. However, from what I've read of the patch that doesn't include the DirectX "conformance" portion that I described. I am also under the impression that I'd have to write a lot of unit tests, which takes time. Then, there's the whole getting code by Alexandre thing. For a lowly student like myself, that may not be so easy. :-)