The founding premise of this article is that "you get more done just before you go on holiday" which I've never noticed. I also think it's inaccurate to assume

The founding premise of this article is that "you get more done just before you go on holiday" which I've never noticed. I also think it's inaccurate to assume that folks generally have "hidden capacity" that will miraculously allow them to get done in 4 days what would normally have taken 5. All this boils down to is profit margin on your work: if you're able to build a pricing model where you bill clients enough to fund 15 people taking an extra day off per week, then you can move to a 4 day work week. If not, you can't.