While the Proton compatibility layer already has DXVK for translating DirectX 9/10/11 into Vulkan, VKD3D-Proton has become the official version for translating Direct3D 12 on top of Vulkan.
Are you confused what Proton is? See our dedicated Steam Play page for info.
VKD3D was originally a project created directly by the Wine team, the compatibility layer that Proton is built upon. However, the original founder passed away and it seems Valve-funded developers are taking the torch to push it much further. It's actually been a thing for a while but today they adjusted the name of their project as VKD3D-Proton, to give it some official status plus preventing any naming conflicts elsewhere and just be clear about their goals.
They're going for supporting the "full" Direct3D 12 API on top of Vulkan, with an aim of both performance and compatibility using modern Vulkan extensions and features, so this comes at the expense of compatibility with older drivers and GPUs. They're also not looking to keep backwards compatibility with the original vkd3d.
Recently, the project also merged in code to allow for a standalone D3D12 build. Like with DXVK, we might even see gamers on Windows using it in future. Yes, that's actually a thing and there's many more like it as it can boost performance on Windows too for older games.
See all the details on the updated VKD3D-Proton page on GitHub.
With the recent news that the massive Cyberpunk 2077 is going to be DirectX 12 only, perhaps VKD3D-Proton can get into a state before release where it might run it well on Linux, since CD Projekt aren't likely to bring it to Linux officially.