It probably wouldn't be practical for small companies, but what I'd really love would be a rotating third day off that moved between Monday, Wednesday, and Friday. I don't think it'd make sense to rotate through all days because having it on a Tuesday or Thursday would just be annoying to go back to work for one day before having another break day.

With a MWF rotation you'd get 4 on, 2 off, 2 on, 1 off, 2 on, 2 off, 4 off, repeat and having that four day weekend every three weeks would really open up weekend trips that require more travel.