The article is all about the upsides of it. But it is necessary that people can afford it. I am already told by a young colleague that he also wished he could work 80%, but could not afford it.
So I think it is a good thing for people who make more than enough income, but perhaps don't really realize it. But it should be an individual choice to do cut down your hours.
I thought the whole point of this forum was about figuring out how to spend money more efficiently so you have a surplus. Presumably, that person is not talking about "It would cut into my savings rate" with "I couldn't afford it."
If you default to the "Monthly net zero" approach to spending, and are spending 40h/wk of income, of course you can't afford less income. :)
I've done an 80% schedule at various points, and it's awesome. Depending on tax brackets, the total hit to takehome is less than expected, and the ability to get things done "in town" on Fridays when everything is open is awesome. Plus, three day weekends. Except for all those four day weekends. There's also more time to do stuff around the house/property that might otherwise be hired out. Lawn service? Nah, I'll just do that when everyone's at work on Friday. Same for assorted improvements.
And, honestly, I'm more productive at work on a 4 day week. If I'm left with a thorny problem, I can think through it on the weekend while I'm doing something totally unrelated to it and have things to try when I get back to work.