The way I read the "Intended Audience", I think the use cases you mention are non-goals for WTF-8:

> There is no and will not be any encoding label [ENCODING] or IANA charset alias [CHARSETS] for WTF-8.

The goal is to ensure WTF-8 remains fully contained, so that ill-formed strings don't end up processed by systems that expect well-formed strings.

If you need to serialize every possible Windows filename, then you must also own the corresponding de-serializer (ie make your solution self-contained), and cannot expect users to work with the serialized contents using tools you do not control.