For me it would be little bit more difficult than 4-day work week. I do agree that 7-8 hours of programming per day isn't optimal for concentration, but having a possibility to have extended weekend is a big plus for me.

I am sure you would find people that adapt to it.

One thing I am wondering is that should everyone work on the same schedule? I am not talking about night shift type of things, but there should be more than enough overlap between working schedules if one works 9-5 Mon - Fri?