I wish these stories would say if the hours are changing or not. 32 hours, 4 days a week seems better to me. But if all you do is take 40 hours and make it 10 hour days I’m not that much happier.
I have had friends and family that work 4x10s or even 3x12s and they all vastly prefer the trade-off of more hours per work day for fewer days.
Tasks expand to take up the available time, even if usefulness doesn’t.
I suspect you’d see little loss in cutting down to 32/hr/week, and I suspect it would be more than made up for by the gains of giving people that extra day. So it may be a net positive.
I guess my main concern is that a lot of companies (not speaking about Japan here, just the US) might decide to use four days a week as a way to make people crunch four days thinking that having three days off would make up for that. And things wouldn’t really be any better.