Since birth rate is below reproduction in most of the world, and population declines (slowly or faster) basically everywhere in the "developed world", even including China, there will be fewer and fewer "other people".
We'll have to produce less and less if we do not keep replacing existing stuff with new (hopefully superior) stuff.
And this is a big deal, too. We've made huge strides in cars and appliances. Outside of specialty needs furniture and carpentry hasn't changed much over the years.
> there will be fewer and fewer "other people".
This is going to take a long time (when measured over the typical human lifespan), and won't be very noticeable outside of child-oriented institutions. Major changes in industries and other events that prompt large numbers of people to move will still be more noticeable.
The transition of Japan from a fast growing "tiger" to a society with few children, older people dominating, and contracting industry occurred very much within my lifetime, and I'm not an old person yet.
We'll have to produce less and less if we do not keep replacing existing stuff with new (hopefully superior) stuff.