Turns out that the intersection is already a huge advance over WebGL, and that much of the stuff outside the intersection is of marginal value or even outright regrettable.
I have followed the WebGPU CG discussions about differences between the APIs and what features one has that the other doesn't. The initial goal of the API is to have a solid core, and not rely on extensions for important functionality. But it does have an extension facility so I'm sure some things will make it in as extensions over time.
