Sounds like a good idea, depending on how it's executed.
Worth noting that when the U.S. Fair Labor Standards Act was passed, setting the workweek at 40 hours, the highest the Dow Jones Industrial Average (a pretty good if not perfect indicator of productivity) had ever stood was 381. The DJIA is now over 16,000. Most of the increase in productivity has come from workers, most of the benefit has gone to owners. One way to even that up is to give the same pay for less work.
Further, a routine four-day work week (personally I'd go for four days of 8 hours each, rather than five days of six hours each), will increase leisure spending by the working and middle classes, with attendant economic benefits.
This experiment is worth trying.