At that point, why not just move leap seconds entirely into local time as part of the time zone offset? Track each time zone’s initial, current, and (inevitable for at least some locales) final leap second offset. Include it directly in the numeric expression of the offset. Freeze UTC at the initial offset, update the relevant specs to provide for this, and call it effectively “done”, where “done” is that leap seconds are an entirely human-facing, local-jurisdiction-governed concern, entirely derived from monotonically incrementing base time.
