OpenUSD is a way of bundling and specifying the data to be rendered. It doesn't relate to which API the app uses to accelerate rendering. Adobe, Autodesk, Blender, and most others support different backends per operating system including Metal on macOS already.
While not at the kernel level I think WebGPU is probably better than something like Vulkan for that "I can target this low level access to the GPU resources but expect it to work everywhere" use case. Ignoring the name hint that it was designed for the web (it works fine outside the browser), it's a lot more portable than Vulkan across its various implementations precisely because it needed to work on various devices that could browse the web. It's also already backed and supported by all the big players, including Apple.
WebGPU, unsurprisingly, is much better supported by the web ecosystem right now (just like WASM in the beginning), so you'd have better luck trying to use ClojureScript (as then you can just use the JS interop) for playing around with it. https://codelabs.developers.google.com/your-first-webgpu-app would be easy to get started with and translated to ClojureScript cleanly without issues.
Also, keep in mind that WebGPU only been around since 2021, and wasn't actually enabled in Chrome until this (2023) spring, so it's relatively new tech, not surprising that the ecosystem still feels halfbaked.
I'm a big fan of webGPU. I use it within my Three.js projects. Really happy to see it gaining support worldwide. I hope either it or similar projects continue to gain traction!