It's not about making people "happy." It's about giving them more time to pursue whatever they want, be it happiness, profit, or world dominance. It's also about accommodating the increasing disconnect between number of workers available and meaningful jobs for those workers.
I don't think the number of days (less or more) is what will make the different. As humans we are almost always going to complain about wanting more or less of something.<p>I know that for me the things that make me happier are:<p>- more efficient use of time
- more effective processes (very much tied to the above)
- percentage of time dedicated within the workweek to personal projects that might be far removed from the actual job or have a very long-term upside
- more focus on the output rather than how/when the job got done. Note: I'm absolutely not saying here that all means justify the end.