There are no cross-platform APIs for something as simple as "blit a bunch of pixels to the screen" anyway, so WASI is pretty much free to define its own.
I'm sure over time, and if desired, WASI will get a set of higher level platform-wrapper APIs for rendering, audio, input and networking, but the requirements are somewhat different from traditional "native" APIs, for instance, compatibility with web APIs is useful. So we'll probably see the WebGPU API for 3D rendering, instead of Vulkan, D3D12 or Metal.
I'm sure over time, and if desired, WASI will get a set of higher level platform-wrapper APIs for rendering, audio, input and networking, but the requirements are somewhat different from traditional "native" APIs, for instance, compatibility with web APIs is useful. So we'll probably see the WebGPU API for 3D rendering, instead of Vulkan, D3D12 or Metal.