bpo-33408: Enable AF_UNIX support in Windows by paulmon · Pull Request #14823 · python/cpython
These changes are incomplete, but this seems like a good point to get feedback on what I've learned so far.
Tests in test_asyncio are failing because create_unix_server and create_unix_connection are not implemented for Windows on the ProactorEventLoop class.
Linux implements create_unix_server and create_unix_connection on the _UnixEventSelectorLoop class, and the implementation cannot be simply copied because Linux uses signals, which don't exist for Windows. Windows appears to uses IO completion ports to achieve the same results.