Unfortunately I did not get to this before the 3.4 beta release, so no, it won't be fixed in 3.4.

You can work around it by overriding collect_incoming_data in your subclass and doing data.decode('ascii', 'surrogateescape') instead of str(data, 'utf-8'), and then doing mydata.encode('ascii', 'surrogateescape') at the point where you want to turn the data back into binary.