[DougGwyn]

If you changed UTF-16 to UTF-32 or UCS-4 I'd support it. I think there are already implementations that use the replacement character for all "impossible" codes.

[hsivonen]

What’s your use case for UTF-32?

[DougGwyn]

There are several multibyte character manipulations that are easier if there is a uniform-sized encoding (wchar_t).