It's likely there will be a need for a C++-level meta-API that can work on top of Vulkan, D3D and Metal. There's already been discussion of making such a thing. It would be nice if that could be exposed to WebAssembly via Emscripten.
The whole point of Vulkan/Metal/DX12 is that since GPUs have their own MMUs it's totally OK to seg fault your own process from the GPU side. You just crash your process, but you don't take down the system.
That line of thinking doesn't really translate well to a JS API.