In work in
ARROW-840, a static arrow.py_extension_type name is used. There will be cases where an extension type is coming from another programming language (e.g. Java), so it would be useful to be able to "plug in" a Python extension type subclass that will be used to deserialize the extension type coming over the wire. This has some different API requirements since the serialized representation of the type will not have knowledge of Python pickling, etc.