How are systems being notified of the leap seconds now, that wouldn't immediately enable them to update their hypothetical leap second table?

It seems like we already have a much bigger lead time for notification than we could possibly need.

> I can see why people don't relish the idea of requiring similar tables just to keep system time accurate.

But the 'solution' we're using now is to make system time less accurate, not more accurate. Accurate would be if leap seconds incremented the system clock like normal seconds do. If the accuracy you're worried about is displaying a clock time rather than time since the epoch, you already need a time zone to do that.