Some of the proposed struct module additions look far from straightforward;  I find that section of the PEP significantly lacking in details and motivation.

"Unpacking a long-double will return a decimal object or a ctypes long-double."

Returning a Decimal object here doesn't make a lot of sense, since Decimal objects aren't generally compatible with floats.  And ctypes long double objects don't seem to exist, as far as I can tell.  It might be better not to add this code.

Another bit that's not clear to me:  how is unpacking an object pointer expected to work, and how would it typically be used?  What if the unpacked pointer no longer points to a valid Python object?  How would this work in other Python implementations?

For the 'X{}' format (pointer to a function), is this supposed to mean a Python function or a C function?

What's a 'specific pointer'?