I must admit, I've always thought this would make sense as well. Now I don't proclaim to be an expert in these things but what with how busy life seems to be these days I've often contemplated how nice it would be to have a 3 day weekend.
Currently working 5 days a week (40hrs), it's just too knackering to do stuff mid week and the two days of rest fly by when you are busy using your free time to catch up on all the routine stuff that live throws at you that you don't have the time to complete in the week.
Especially now as you consider that even Sundays, previously considered to be a day of rest, many businesses and other daily activities continue to go ahead. We really are a 24/7 society.
How it would work realistically? No idea, probably wouldn't. But in theory it would be nice to either create an extra day for the weekend or make Fridays a non working day. It would never happen though.