[MAL]
>  * Unicode objects are NUL-terminated, but only very external APIs
>    rely on this (e.g. code using the Windows Unicode API). Please
>    don't make the code in unicodeobject.c itself rely on this
>    subtle detail.

I would like to note that several APIs have been introduced that require NUL-terminated unicode strings: Py_UNICODE_strlen(), Py_UNICODE_strcpy(), etc.  I see them used quite extensively in unicodeobject.c and elsewhere in Python codebase. Perhaps this train has left the station already.