4 day work week coming to a job near you?...

I agree. We went to a 4-10 work week during Covid, in 2020, it was supposed to be a temp thing, but after realizing how much better it was, they made it permanent. Although I love being off every Friday, working those 2 extra hours a day took some getting used to.
I would love to see a 32 hour work week with no reduction in salary, but i seriously doubt most companies are willing to do this, in the USA.
I don't think most companies are willing to do it in most of the world, but that's because most companies are, to put it bluntly, dumb.

As far as I know, a 40 hour week wasn't determined to be the optimum amount for all types of work, it's just kind of emerged from employers wanting people to work all the time and workers not wanting to and demanding things like weekends (e.g. I don't know about the US, but the two day weekend was only established in the 1930s here).

When they tried that two day weekend, they found efficiency improved and absenteeism reduced. Which is similar to what they're finding with four day week trials. Because the thing is, people not being machines, if you try to get people to work more than they can optimally sustain, they end up working badly (or not at all if they can goof off), making mistakes, and/or wearing out.

So if, for any given job, four day 32 hour weeks are actually more efficient, companies absolutely should be willing to do it. That they're reluctant to do so says more about the systematic behaviour of companies than it does anything else. But maybe it'll happen. After all, the two day weekend did. Eventually.