The tests I’ve read about in recent times have not netted a loss in pay - simply a reduction in hours but an increase in productivity because workers are well rested and happier with their work life balance.
Again - what you’re describing already exists, it’s called a part time job. If it comes with a loss in pay, then how improved is your work life balance when you have to go get a second job to supplement your income as a result of transitioning to a 32 hour work week? And how much more productive are you going to be if it means you’re now working a 6 or 7 day work week?