"00:00:00 on January 1, 2020, local time", if it is to represent a calendar event in the human work day in the future, should be represented as neither a TAI "timestamp" nor a UTC "timestamp", but as a data type containing exactly "00:00:00 on January 1, 2020, local time".

> But updating all time conversion software (instead of just updating authoritative clocks) every time there's a leap second is ludicrous.

All time conversion software is already updated every time a government changes a time zone - by downloading the most recent tzdata. All software that needs second-level granularity is constantly updated, by synchronizing with NTP. There's nothing at all ludicrous about distributing leap second tables instead of mutilating the NTP time signal.