The mental overhead is pretty significant.

You need to do weird string operations, you have certainly a class somewhere that needs to append a zero to then end of a buffer, and exclusively use the class for thw filename. You can't just toss a contiguous number of bytes you to convert it first.

Every single piece of software that need to interact with the file system needs to deal with this.

I'm not asking about a new string type. I'm asking to be able to be free from null terminating string.

You only need to provide a length.