Then Again we ae talking of a Company that has investes alot on it's own Graphis engine (Cobra) and that is very buddy buddy with Microsoft ... so dropping DX in favor of a open source platform for Windows players, might not be on the road, making (cobra) compatible with Vulcan API, is a good idea because it opens even more market for Open Source S. O.'s , although we have not seen Frontier show much interest in open source S. O.'s!
Correct me if i'm wrong Frontier !
Currently, they need to support DX 10, DX 11, OpenGL for Mac and whatever the consoles use. DX 12 would introduce new features, but would exclude the significant number of Windows 7 players. A migration to Vulkan would give them "next generation" features and reduce the number of supported APIs drastically.
Vulkan is available for all versions of Windows (7 through 10), many people have it already installed (i.e. everybody with Nivida cards). Support for macOS is available through a third party and could be licenced. That might address the OpenGL gong show on the Mac. Vulkan also seems to be available for the PS4. So all these platforms could be supported with the same API. Bringing down the number of graphics APIs from 5 to 2 seems to be very attractive to me. As a by-product, a Linux version should now be super-easy to do.
Cobra is a framework and very modular (it has been around since 1988!), so adding/replacing the graphics API is something they have done before.