A 4 day work week can always be implemented as 4 10 hour days instead of 5 8 hour days.

> Who wouldn't be a fan of 80% of the work for 100% of the pay?

If you, as an employer, want a motivated, energetic workforce who are not slacking off, it's also in your interest to give that opportunity to your employees, as multiple experiments have shown that 4-day work results in increased productivity and employee retention.

Knowledge work does not have 1-1 correspondence between time spent and productivity. Things get VERY non-linear, to the point that more than 50 hours of real knowledge work a week is often LESS productive than 40 hours.