So FYI I’m a developer for AMD, and helping with this HIP work for cycles-x. I don’t mean to be gatekeeping but this is a developer forum. Probably not the right place for speculation about what other platforms, (vulkan, metal) etc could be possible.
The info above about HIP is part of the bi-weekly cycles meeting update. When we’re ready to say more publicly about HIP support in Blender and answer all your questions it will be coming from somewhere else for a wider audience. Please have patience, this is just meant to keep developers updated!