I don't think private companies going to comply with 3 day weekends. They will deduct one day salary every week plus working on Friday with petty excuse that client requires you to work.
I am all for the 4-day weeks if I am honest but I do not see it ever becoming a possibility for all if I am honest mainly due to the fact that many companies will not comply with a 3-day weekend. I know here in the UK some companies do not even allow a 3-day weekend when there is a bank holiday so in which case having it be a regular thing would definitely be a no go.
Do I feel a 4-day week would be better for people in terms of rest and not feeling of burned out? Yes, definitely. Unfortunately, companies will look at it from a money perspective over the health of their employees.