Spouses work these days and more and more people choose not to have kids, optimizing for _their_ life quality rather than someone elses. So I wouldn't say that stress only increases. Stress only increases if you want the stress, otherwise I'd say stress decreases and a person has more and more savings, can afford better life quality, etc.
It's been decreasing so far, with financial safety, a saner schedule (no more absurd school deadlines for subjects I don't even care about), and more freedom of movement (one gets pretty isolated with no car in my area).