These employers have introduced four-day work weeks and 'can't think of a downside'

Now we wait 10-20 years for the rest of society to catch up

They obviously don't work in a service industry then. Sure it's fine for non customer facing employees. But if you work in a cafe for example, or for any small business that can't afford more staff to cover your extra day not being there (as they must remain open), then that's it. The idea is GREAT, but, it can't succeed for so much of society.