Paul Eggert <eggert@cs.ucla.edu> writes:

> The idea is to add a new \X escape for character constants and
> strings. This escape would allow at most two hexadecimal digits,
> rather than the unlimited number of digits that \x does. For example,
> the Lisp string "\XABC" would be equivalent to the Lisp string "\xAB\
> C", that is, it would be a two-character string containing the
> character U+00AB LEFT POINTING GUILLEMET followed by the character
> U+0043 LATIN CAPITAL LETTER C.

This was four years ago, but I don't think any steps were taken in this
direction, beyond marking the raw bytes more clearly: