Re:WebGL on WebGPU
Chrome's GLES compatibility layer for Vulkan, Metal and DirectX is available at https://chromium.googlesource.com/angle/angle. Mesa also has a backward compatibility layer for LavaPipe but I don't remember what it's called.

Going from a low-level API to high-level is much harder than going the other way. OS 4.1's Warp3D Nova is a thin wrapper around SPIR-V shader API (or so I've heard) and has a GLES 2 layer that comes with it.

Of course Google wouldn't bother hosting a Warp3D Nova implementation of WebGPU but having a low-level API of some sort delivers better results on some configurations.

This thread is starting to converge with the other one about Warp3D Nova so I'll leave this as is.