At the very least, could it be feasible in a small organization to stagger it so that some people work M-Th, and the others T-F, so there's partial coverage for all days of the week?
I'm the CTO and have set up alerts that I get on my phone when I'm not in the office, so even if something critical happens over the weekend it's not like I won't fix it for 3 days.
I noticed that I'm more motivated during the 4 days to do a maximum of stuff, I take less smoking pauses during the day, which increases my productivity and is better for my health ;). I also have no problem to stay one or two hours longer on thursday evening if something needs to be done before the long weekend because I know I will have plenty of time to recover afterwards anyway.
Also in my opinion no solution reducing the amount of working hours should have disadvantages over the conventional 5 days / 40 hours weeks, or there will be no produtivity / motivation gain. So just saying we still work 40 hours but do this on 4 days a week is obviously bad. Also working 32 hours and being paid less is bad and so on...
Something else that had a huge impact for me, is that our working hours are much more flexible now. We have four so called "core hours" from 10 in the morning to 15 in the afternoon where everyone has to be in the office, the rest is flexible. So you are allowed to work 7 hours one day and 9 the next day. Also you can include two one hour pauses as long as the minimum amount per week is not lower than 32 hours. For me this is great because it allows me to drive to work and from work when the traffic on the streets is much lower than at peak times where all the other workers commute.
Moreso as the time allotted goes up and the arete of life goes down.
My most productive, correct, happy, focused work comes when all of my needs are met excellently and when I feel like it. You can't tell me when to have a very good day of work, but the more you take care of me, the more often, intense, and extensive my best days are.
40 hour work days are for drones, slaves, people doing mindless or obvious work. I'll call that Drudgery. Its opposite I'll call Art.
Hire a painter to create new works, 9-5, and you'll get something which with shallow judgement looks like art, tries to be, but is simply not. Become a patron of an artist and you might get something real.
People are learning that art is not drudgery and when you confuse the two you get bad quality work, inefficient work, and bad quality life.