If you just care about GPU compute and not much about the shape of the API or it's overhead, then something like OpenGL ES 3.1 Compute Shaders or WebCL would be much easier to reach than WebGPU, technically.
Mozilla won't support WebCL in favor of compute shaders, but that announcement has been over 4 years ago and there still is no general compute in browsers: https://bugzilla.mozilla.org/show_bug.cgi?id=664147
