I really don't like the _NEW suffix, as in SO_TIMESTAMP_NEW, opposed to the normal SO_TIMESTAMP64 naming scheme, as in the function names. But it renders the existing names as old and outdated, so it does make some sense.
Personally I'll wait for SO_TIMESTAMP_NEW_NEW_FINALTHISTIME.
It only makes sense from a shortsighted "today's" perspective. What happens if there is another API change? Do you call the new new suffix _NEWER? _NEWNEW?
Thanksfully 64 is the endpoint. "We'll never need 128bit time_t struct's!" Famous last words. But really, we don't. We don't need to mix low precision with high precision times, "one for all" . Calculating in ns does not make sense in the year scale.