> [P]eople that aren't interested in having children will 'go away' as the population declines, and we will reach a new stable population level?

I think this is exactly what we're seeing. This is evolution as a punctuated equilibrium. Nature's last trick "sex feels good (but also leads to babies)" is breaking down in effectiveness on people. Instead, it will be some innate desire to have children that will carry some subpopulation forward. Given the extremely strong selection pressure on (it affects the one life event most determinative of "evolutionary success") this could happen really quickly.