BOM goes the bank balance
It is hard to forget the fact that Vega is more than a year late. It was supposed to launch last year and AMD had to settle for Polaris 10 and 11 performance mainstream / mainstream parts.
Sometime in the future
In a press release which announced OpenCL 2.2 and SPIR-V 1.2 finalized specifications, Khronos Group hinted that it might merge OpenCL with Vulkan API in the future.