Chris Roberts hired CRYENGINE devs to work on the engine specifically for Vulkan and DX12 (this is why the CRYENGINE has support for these APIs).

Chris has mentioned they had already added patches awhile back for Vulkan. But they plan to get DX12 setup first before Vulkan.

But I wouldn't be surprised if it ends up being the other way around, considering Vulkan will help those on win7,8 and Linux. were as dx12 only pertains to those on win10.