In your letter dated Wed, 24 Jun 2015 14:05:34 +0100 you wrote:
Philip Homburg <pch-nanog@u-1.phicoh.com> wrote:
For UTC the analog approach would be to keep time in TAI internally and convert to UTC when required.
This is much less of a solution than you might hope, because most APIs, protocols, and data formats require UT. (Usually not UTC but a representation isomorphic to traditional UT which ignores leap seconds.)
Supporting legacy formats can be annoying. In some cases it would be no problem. For example NTP. If there is a defined way to convert between TAI and UTC then converting TAI to NTP timestamps is easy except during an actual leap second. Which is not really a problem. Unix systems would probably need a few new system calls to accept time in TAI. File formats like tar are unlikely to matter much: find a consistent way of encoding time around the leap second and most likely nobody will care. In any case, it would be nice if future formats and systems could have a sensible time keeping system.