"We make the case for a general reduction in working hours __without__ a reduction in pay. We also make the case for a steady managed transition to shorter hours with a bolstered welfare state in such a way that the most vulnerable and underpaid in society are protected."
It's hard enough to ask companies to shift to a 4-day workweek for the various reasons outlined in the article and sibling comments, but usually this is accompanied by a corresponding cut in compensation. Adding the "without a reduction in pay" condition makes the proposition much more difficult for small-to-medium sized businesses.
In fairness to the article, there is the possibility of asking employees to work 10hr workdays for 4 days to accommodate the 40-hr work week model (or 8.75hrs/day in France to accommodate their 35-hr work week). Since (most of us?) are already overworked, maybe this then just boils down to a scheduling and staff coverage problem.