How would our society handle five million, or ten million or thirty million people who would – because more and more jobs have become obsolete – simply have nothing to do?

Simples: Stop counting them and they cease to exist.

(And if they don't disappear from view, let the SA have some fun in the name of health & safety once in a while. Oh, and remove park benches, or add dividers. And plant spikes in the doorways, under bridges, etc.)