If one believes that less time spent working increases productivity, then by all means let's go down to 1 day a week. We'll see HUGE productivity gains there... right?
After trying something similar I think it might be better for people like me to work really hard M-T, take a breather on W, then hit it hard R-F. Thats a very different rhythm than slugging M-T-W-R-F week after week.