4-day week would be a thing for example when employers out of desperation for not being able to find workers start enticing borderline great resigners by 4-day week (so you get all the benefits of full time employment: health insurance, pensions,...). But this is assuming workers continue to have the upper hand.
Maybe, but it seems most industries couldn't do it without a massive increase in workforce, but worker shortage is what they're trying to fight. Unless the entire industry switched to a 4 day week, I don't see it working out for most. I'm mostly thinking about places ties to central things like the stock exchange for banks, or that need 24/7 support like police and nursing, or where manufacturing wants the machines to run close to 24/7 to be economical efficient (since we struggle to compete already with LCOL abroad).
Even if all your employees worked 4-days week doesn't mean your business opens only 4-days week. You simply ensure the amount of workers who are off on Monday is the same as the number of workers that are off on Friday. You only need to increase headcount by 20% if you make all your employees 4-days week. Which is a lot but not a "massive increase", especially you will be paying them 20% less each.
