Why should this excite me? Wine already can do DX9 pretty good. And according to one comment this does not even compare. Who cares about DX9 nowadays? DX10/11/12 would be very different story. Something like this bringing modern windows games to linux would be great.
Even greater would be M$ open sourcing DX but that will not happen in the next few years.
I would assume that performance would be low-hanging fruit. OpenGL and DirectX work quite differently, so translating the calls of one to the other should involve quite a bit of work/CPU cycles. Vulkan, being closer to metal, should be a more straightforward translation target.
Example: HLSL-to-GLSL is likely a difficult problem, where HLSL-to-SPIR-V is probably much simpler.
> Who cares about DX9 nowadays?
Lots of games still support it. In addition this layer could be used for future work in DX11/DX12, instead of the (per my above argument) more complex OpenGL translator.
What good would open-sourcing DirectX be without the Windows Display Driver Model? And how easy would it be to get that working without the NT kernel? And how interested would the Linux kernel be in supporting this?
> What good would open-sourcing DirectX be without the Windows Display Driver Model? And how easy would it be to get that working without the NT kernel?
Shouldn't be harder than what Wine is already doing. Open sourcing can surely help in some ways. MS for example already open sourced HLSL parser, so translation tools can benefit from it.
What about older games? I think this would make it possible to improve graphics of those games by going trough Vulcan and adding new features to the pipeline. With Steam and GOG there is a big market for older games and for older games with renewed graphics and up to date compatibility.
Even greater would be M$ open sourcing DX but that will not happen in the next few years.