There's also a precedent of us breaking socket API.  In Python < 3.6:

  sock = socket.socket()
  fd = sock.fileno()
  os.close(fd)
  sock.close()

Everything works fine.  In 3.6+:

  sock.close()  # Will raise OSError

uvloop broke on this during the beta period and I fixed the issue quickly.  I don't remember seeing any complaints about this, so I suspect that this issue wasn't a big deal, people just fixed their code.