We need to keep an open mind about this. Someone upthread mentioned education. My SiL, a secondary teacher, has opted for a 4-day week already. His subject, English, is now experiencing shortages and is especially marking and planning intensive.
The extra day ‘off’ allows him time to catch up on planning and marking from home. And, interestingly, the school has found it easier to recruit other teachers on a part-time basis. I’m hearing more and more of teachers solving their workload problems in this way.
It is true that some workers, would prefer the option of a 4-day week if they can cope financially. It is certainly not a problem for shops etc. to recruit on a part-time basis especially if that is PT and permanent.
I’ve been retired now for 13 years and even before then quite a few of my team chose to work on a PT permanent contract, usually 4 days. It didn’t mean they all chose the same days but the nature of the work meant there wasn’t an issue.