At the moment, that looks like Amish, Muslims, and Elon Musk.
The population who remain childless to not add to the population burden of the planet will become irrelevant. I find that sad, since I really like several of them...
No, Musk lacks something the Amish and Muslims have: continuity. Amish children are likely to remain Amish.
Musk may have 20 kids but those kids will probably have the American average of 1.5 kids each and his descendents will limit to 0 like everyone else in his culture.
What does this mean? Are you saying the human population of the universe will drop to 0? If so, why mention "his culture"?