System call conversion for year 2038

That would seem to militate in favor of separate time formats for "point time" (timespec) and "interval time" (u64 ns) - as has occurred in more modern date/time libraries, such as Joda Time.

Furthermore, at that point "now" could be defined in an offset-ish way - use point time for "when we booted" and interval time for "...and how long has it been since then?"

But that'd be an even more drastic API change, and thus deeply unlikely.