Any country can't afford more holidays. I like your idea for family holiday, friendship holiday etc as golden day but it will disturb every second factory where workers need to work consistently. Those countries in which 3 day weekend is implemented are lucky, we are away from this concept because we have only two day holidays..
I understand that an extra day in the month for the worker to rest would result in great harm to the place where he works, if we think that there would be 12 more days of rest in the year, it seems not to be such a bad thing, but it depends on the what each place does or the industry it follows, then it really is a complicated matter.
Regarding the 4-day week, I believe that this is more tangible, as there are several places that are already testing this and it seems that it really works, so it may be that in the future this could even be implemented en masse in the future. I hope that happens 😂