> …the next which is expected in roughly a 1000 years: https://www.ucolick.org/~sla/leapsecs/futuredelt.svg

Which doesn't seem like that is soon, but time/calendar issues can creep up and then it's a big hullabaloo:

* https://en.wikipedia.org/wiki/Gregorian_calendar

It can be handled like DST changes and/or changes in time zone rules. Software based on the tz database should already be able to handle it.