Maybe people could take different "3rd" days off?
I have a friend who once had M-W off, and worked the four remaining days. He hated it because his time off was completely misaligned with his peers, so he had no social life.
Edit - I don't have any fundamental problem with working fewer hours or fewer days. But, I think I'd prefer 5x7 hour days instead of 4x8.
I can imagine there are plenty of other people that prefer the same thing.
Having tried both, 4x8 is far better. I don't do much during 5x7 evenings anyway because I'm drained after 7 hours at work, so I'd much rather just cram that into 4 days and have an extra day of rest.
Rotate who gets which days off each week.