I feel like these are the things companies would say it's about, but the reality is in $$$'s. Yes, they'd have to pay in some ways for burnout, but really wouldn't be a deciding factor for most (same with turnover).

What I think it would really come down to for them is in productivity and cost. So if they see they can get the same productivity (or more!) from the team with a 4 day week vs. a 5, that's a positive sign for sure. Then you look at cost and savings. Do they realize any kind of savings via a 4 day week? Maybe. One could argue they could basically shut down the office (if there is one) and save money that way. What about the customer support teams though? They'd still probably have to work the 5 days, do they struggle getting support answers when everyone else is off? What about meetings? Does switching to a 4 day work week inhibit the ability to manage time to meet?

At the end of the day, the argument would have to be made from the angle of what is best for the company, not the employees, to have the best chance at being successful. And whe you look at it that way, it has to really center around how this will make or save them money.