Can the current demographic collapse give opportunity for a humane eugenic boost?
Since most people don't want children at all, people without history of genetic diseases, and tendency for higher intelligence/strength could be offered money in exchange for having children.
I am not defending that everybody else should be banned from having children, just that since they are already doing that and it will cause long term problems, demographic stabilization could be achieved by incentivize the healthiest ones to have more children.
I think it has more impact when, for example, you remove wars and poverty than anything else. Because the world transportation and worldwide easiness of traveling is so high today, the ability for control is very little.
I don't think it would have significance in terms of numbers. Probably that already happens anyhow. People who have money look for people who have money, as they have historically. And they are even prone to pay the extra price even if the person has problems due to affection.