>If filesystems are using binary data for filenames, there can be a case when is really no way to address a file by typing its name, even if you can type in that language

You could do that trivially in UNIX since forever.

Don't know about other UNIXes, but at least on GNU/Linux, neither IMEs nor filesystems are working with text data - it's all binary strings (with a few restrictions, like unacceptability of NULs). The only place where those binary strings are converted to text is when they're rendered (and this may cause some encoding-related oddities). So, sure one can do that.

I would've actually preferred for identifiers to be Unicode text strings.

Filesystems themselves treating file names and paths at bits of binary data is the right way to do it, normalization shouldn't be handled directly by the filesystem as it adds complexity and duplication of effort.

Ideally, the VFS layer should be handling all this garbage.

Programs often allow you to type arbitrary binary values using a keyboard, either by holding a keyboard control key and typing the numeric value, or prefixing it with '\'.