sesam :
All major developers should shift to Vulkan. Unless Microsoft hands you a bag of money it does not make any sense to support DX12. Vulkan has similar or better performance and multi OS/platform support.
Vulkan is about a year behind DX12 feature wise, and MS continues to add features with updates. As is usually the case, when MS is motivated, they "oddly" increase their rate of development and quality. As older Windows OS's are phased out, and 10 and whatever else is coming become the standard, Vulkan will turn into the next OpenGL. Also, some of Vulkan's comparable features to DX12 also require Windows 10, since the features require WDDM 2.0 to work.
According to Steam, about 0.79% of gamers are using Linux. Somehow, I doubt Cloud Imperium is using Vulkan so they can target that market. Microsoft OS's own the gaming market, so acting like you using Vulkan is somehow breaking free from the MS prison is missing the forest for the trees. The platform support benefits of Vulkan vs DX12 right now is that Vulkan supports older versions of Windows, though again not with all features, which is still tying you into Microsoft. But whatever helps you sleep at night.