Let's be honest, the real mess is with UNIX filenames. I dare you to come up with a legitimate use case for allowing newlines and other control characters in a file name.
It's like a built-in unit test - devs have to not mangle and assume anything about filenames they get from the system - though they still do, I've seen multiple times how my nice umlauts get mangled or my spaces cause scripts to fail.
A few years ago I tried naming my home directory with the unicode pile of poo () and a space in the name to test what of my code might break. However, it broke too much of third party tools/scripts that I occasionally needed for something, so I reverted within a few days.
Though it might be interesting to have an integration test box where the username (and thus all the relevant paths) includes all kinds of oddities - whitespace, emoji, right-to-left marker, etc.
Maybe. But 50 years ago utf-8 didn't exist, unicode didn't exist, possibly not even latin-1 did exist. If unix had enforced a specific encoding (which implies constrains which byte values can appear in a path byte string), transition to newer encodings would have been significantly harder.
