1. PyTorch is going all-in on torch.compile -- Dynamo is the frontend, Inductor is the backend -- with a strong default Inductor codegen powered by OpenAI Triton (which now has CPU, NVIDIA GPU and AMD GPU backends). The author's view that PyTorch is building towards a multi-backend future isn't really where things are going. PyTorch supports extensibility of backends (including XLA), but there's disproportionate effort into the default path. torch.compile is 2 years old, XLA is 7 years old. Compilers take a few years to mature. torch.compile will get there (and we have reasonable measures that the compiler is on track to maturity).
2. PyTorch/XLA exists, mainly to drive a TPU backend for PyTorch, as Google gives no other real way to access the TPU. It's not great to try shoe-in XLA as a backend into PyTorch -- as XLA fundamentally doesn't have the flexibility that PyTorch supports by default (especially dynamic shapes). PyTorch on TPUs is unlikely to ever have the experience of JAX on TPUs, almost by definition.
3. JAX was developed at Google, not at Deepmind.