Actually in the top comment of that article it says that the article author had a misundertanding.
What will potentially be merged is the intermediate representation SPIR-V, not the languages on top. I did find something called ["Vulkan Compute"](https://news.ycombinator.com/item?id=11798208). However OpenCL can also run on CPU while Vulkan cannot (yet?). For now, neither Vulkan nor HIP are mature enough, in my opinion it would probably be easier to target LLVM-IR and let LLVM do the SPIR-V compilation.
