...accurate for a period of 158 million years...
It's accurate for 158 million years, and then suddenly loses its accuracy? I don't think so.
Anyway, the obvious way to deal with this is at the point when you convert between UTC and display time, which we already do for timezones.
Right now the offset between BST and UTC is 3600 seconds. That offset should change to 3599 seconds, and UTC should continue unchanged. The TZDATA files will get bigger, but not much, since all countries should implement the leap second at the same time.
However it means you can no longer work out the GMT date by taking a UTC value and dividing it by 86400. So you need to persuade people to use a library call to do that instead. Of course, nobody will bother to do this, so various applications will do the wrong thing for a few seconds a day.
There will be lots of minor annoyances. For example, your telco's billing system, which is supposed to give you free calls at 19:00:00 onwards, will only give you free calls from (say) 19:00:10 onwards, so you'll be overcharged once in a while.
Once the offset builds up to a minute or two, and people are turning up to meetings at the wrong time, they'll be resolved.
But if you're going to decouple UTC from the rotation of the earth, why not do it completely? Let's have UTC decimal time, with a UTC "day" defined as 100,000 seconds.
Biting the hand that feeds IT
