I would step in and do the work you are not doing on the 5th day. We will see how employers deal with this. "I want to work from home, and I want to work less", lets see if this works out for you people...
Look, it works for me. I work Mon-Thu and work from home. My employer deals with it just fine. They have a happy employee and pay a day less a week as well. It's all about communication and organisation at the end. I see a lot of jobs that could be optimised to be done in less than 9-5 five days a week.