[khazhoux]

So then some combination of my points (1) and (2), with the theory that there would be less wasted time during "work hours" and increased focus due to better work/life balance?

The counterargument to that theory, of course, would be that neither would happen, and there would be the same amount of time not getting work done, and people would work at same rate without any increase in focus or motivation. As you said, experiments may help answer this.

There's also another angle of why this is a contentious issue. The idea that people pushing for 4dww are already in cushy jobs with low accountability. Maybe of us here are software engineers being paid $$$$ meanwhile we're spending time writing long comments on HN instead of, say, working on that bugfix that people are waiting for. By contrast, a very large part of the workforce might be less affected by "motivation" than the kind of people pushing for 4dww.