Is stimulation the most important thing in childrearing?
> What is the spouse who stays home supposed to do in ten years when the child is much more independent and at school or activities much of the day?
Volunteer? Find self-fulfillment in something other than a career?
Plus, I think you may be begging the question: while older children require less immediate attention than younger ones, they still require plenty of care. It just tends to be more planning and less direct interaction.
Plus, why do you assume only one kid? My mother spent more than a quarter-century with children at home. She certainly was never bored.
> And what are two spouses supposed to do when they both deeply enjoy their work and the value it brings them as individuals?
Maybe work from home? Ultimately, though, parents today must sacrifice for their children, just as parents have done for millennia. Kids aren't expensive status symbols: raising them well is a duty, not a lark.