Yeah, but also perhaps the 2-day weekend is too short.

It seems way more of a stretch to have a non-regular work "week" of 8 days.

But I'm more skeptical that 5 days is too long vs 2 days is too short.

There is a gigantic difference between 2 day weekends and 3 day weekends. Literally, it's 50% longer.

From a work-week perspective, 4 days vs 5 days is only 20% shorter. And the difference is not that noticeable.

Another possible solution to achieve similar goals is to give workers ~47 Mondays and Fridays to use as vacation at their disposal.

Some people might want to have 4-day weekends for half the year. Some people might want 3-day weekends the whole year.

This is not really a logistics nightmare to plan around for non-service jobs.

Depends on the job. Desk workers, sure, you could get more done in four days than you used to in five. It's not like that for everyone else though. If your job does not involve creativity chances are you do more work in five days than could be physically done in four, unless you go from working eight hour days to ten hour days.

Yeah, I don’t quite see how reducing hours of, say, construction workers, or grocery store clerks can have little or no negative impact on productivity.

I'd say the 47-50 week work-year is too long to be efficient/time productive.