I suggest taking this article with a grain of salt. The assumption seems to be that it's totally fine that Linux can have filenames that are arbitrary byte strings and that don't convert to valid Unicode text. First, Python 3 has a good way to deal with those. See PEP 383: Non-decodable Bytes in System Character Interfaces.

Second, having filenames that are not valid Unicode text (even if Python 3 has a way of handling them and round-tripping them) is going to cause you a lot of pain. No one who has thought through all the issues thinks its a good idea. The modern computing world uses Unicode text all over the place. Filenames are manipulated by humans and we deal with them as text.

The idea that 8-bit byte strings are the ideal way to deal with text is a dead end. I expect we are going to see more of these kinds of articles now that Python 2's EOL is coming. In retrospect, you could argue that Python 3 should store Unicode text in memory has UTF-8. However, at the times decisions were made, UTF-8 was not dominate as it is now.