My original queation was really whether it isn't time to abandon 8-bit-only files except as their encoding is a strict subset of utf-8/unicode.

Just autoconvert iso-1158-1 etc. at the beginning and be done with it.

In the year 2525, if man is still alive, they'll look at a 7-bit ascii file and ask "What's this?" They'll be much more likely to understand a represemtation that includes most of the languages on earth at the time.