As far as I know macOS does not support different salt types at all. The manpage does mention an "extended crypt", but according to the documentation that just controls the number of DES rounds used.

In particular:

    The salt is a 9-character array consisting of an underscore, followed by 
    4 bytes of iteration count and 4 bytes of salt.  These are encoded as
    printable characters, 6 bits per character, least significant character
    first.  The values 0 to 63 are encoded as ``./0-9A-Za-z''.  This allows 
    24 bits for both count and salt.


If anything needs to change it would have to be a macOS specific patch to the _crypt extension that rejects any attempt of using algorithm selection (but that's technically a backward incompatible change as)