To be universally applicable it would have to support at least date, time, time zone and time zone database version (since time zone definitions keep changing).

To be universally applicable it would have to support at least date, time, time zone and time zone database version (since time zone definitions keep changing). You would then have to define how each of these look in a backward- and forward-compatible manner and define what every combination of them means. For example, a time and time zone but no date or time zone database could mean that time of day in that time zone on any day, using the time zone database active at that date and time. Not saying it can't be done, but it's a big job.