Rather than a uniform reduction in hours, the result appears to be a swelling class of unemployed and increasing hours worked by those who are employed.
Those who have time do not have money and vice versa.
From wiki:
"The eight-hour day movement or 40-hour week movement, also known as the short-time movement, had its origins in the Industrial Revolution in Britain, where industrial production in large factories transformed working life. The use of child labour was common. The working day could range from 10 to 16 hours for six days a week"
We now need a 4-hour day movement. :)
These two aspects make sure the majority of people stays unfree and hence doesn't have enough time at their hands for useful work or projects.
I'd say if we can manage to solve this problem we unleash tremendous potential for improving the human condition and life for everyone.
But current events certainly argue against this idea -- if anything, on average people are working more hours now that they did in the past.