Absolutely right about ML being the main motivation. The PEP says:

    The main case this PEP targets - concerns typing in numerical libraries.

However, despite the authors of the PEP working at facebook, the Pytorch team, at facebook, wasn't interested at all in the PEP. This is also from the PEP:

    For the sake of transparency - we also reached out to folks from a third popular numerical computing library, PyTorch, but did not receive a statement of endorsement from them. Our understanding is that although they are interested in some of the same issues - e.g. static shape inference - they are currently focusing on enabling this through a DSL rather than the Python type system