In the limited C API, Py_REFCNT() should be converted to:

static inline Py_ssize_t _Py_REFCNT(const PyObject *ob)
{ return ob->ob_refcnt; }
#define Py_REFCNT(ob) _Py_REFCNT(_PyObject_CAST(ob))

It would enforce the usage of newly added Py_SET_REFCNT() (PR 18389) and advertise that the object is not modified (const).

That would only be the first step towards a really opaque Py_REFCNT() function.