Rationale:

Recommend NAD and fix as editorial with the proposed resolution.

Proposed resolution:

Change [cstdint.syn]:

...
typedef signed integer type intptr_t;    // optional
...
typedef unsigned integer type uintptr_t;    // optional
...

In the synopsis, some types are identified as optional: int8_t, int16_t, and so on, consistently with C99, indeed.

On the other hand, intptr_t and uintptr_t, are not marked as such and probably should, consistently with C99, 7.18.1.4.