Well, Perl 6 also introduces a distinction between strings (Unicode) und buffers (octets), but it also introduces loads of other changes, to the point where it'

Well, Perl 6 also introduces a distinction between strings (Unicode) und buffers (octets), but it also introduces loads of other changes, to the point where it's its own language. That said, the Unicode features were a major thing planned for PHP 6, and (afaict) one of the reasons there has never been a PHP 6, but rather they went straight from 5 to 7. I'm not aware of any graceful transitions.