This is the idea from the Positivist religion, formed as an appeal against our current gregorian calendar. Ethiopia follows a 13 month calendar but its slightly different. The gregorian calendar replaced the julian calendar around the time od the protestant reformation. The main reason for the change was to account for leap years.
Discussion
Couldn't we still have a 8th day sometime in a week every four years and then continue with Monday? Or is this something the bible people would go against?
Or would we even need it or does this leap year day come from the weird rounding in our current calendar?
The leap year weirdness is to account for the true time it takes to make one trip around the sun, it doesnt mesh perfectly with the lunar calendar. That is the main issue with these calendars, either they focus on the moon or the sun. You cant do both, or at least we havent figured out an algorythm that sufficiently deals with both.