Please correct me if I'm mistaken (not a ML expert): On top of these existing APIs, we can build efficient neural networks. Of course, we wouldn't be able to use specialized hardware such as Google's TPU or Graphcore's IPU, but I doubt there's a use-case for those in web.
Is there any non-GPU/CPU based consumer hardware aimed at fast neural networks that I'm missing?
EDIT: Seems "NPU"s have been slowly arriving for the past 2 years to iOS/Android-based devices... Maybe there's a raison d'être for the WebNN API after all.