I fear my example about thinking about `ndarray.__array_function__` distracted from the gist of my question, which was whether for `__array_function__` implementations *generally* it wouldn't be handier to have all unique types rather than just those that override `__array_function__`. It would seem that for any other implementation than for numpy itself, the presence of __array_function__ is indeed almost irrelevant. As a somewhat random example, why would it, e.g., for DASK be useful to know that another argument is a Quantity, but not that it is a file handle? (Presumably, it cannot handle either...)