Valve's Proton Offers Branch With VKD3D For Direct3D 12 Over Vulkan
VKD3D is the official Wine project being worked on for accelerating Direct3D 12 over Vulkan. This has been Wine's only pursued D3D12 approach with Direct3D 12 not mapping nicely over OpenGL and thus not fitting well into their existing WineD3D code. VKD3D has been able to run a few games, but at last check not many though that may be different these days with it already being included into Proton.
As of yesterday, Proton is now building and shipping VKD3D for its Direct3D 12 support. At the moment there isn't any new Proton release out on Steam but this is just the latest activity in Git.
It will be great once VKD3D is as stable as DXVK is to Direct3D 10/11 support in allowing modern Windows games to work nicely under Steam Play on Linux, assuming they don't run into any problems due to anti-cheat software and other headaches still being addressed for improving the Windows gaming on Linux experience. Exciting times ahead.
Update: This work is currently staged in one of Valve's Proton Git branches. The user who pointed us to this commit had (incorrectly) indicated otherwise, so it's not yet in mainline upon closer examination, but hopefully will be there not too much longer.