The French First Republic[1] and the early Soviet Union[2] both briefly reformed their calendars, but in both cases the changes were reverted after a couple of years. There's also a whole bunch of proposed calendar reforms[3], each with its pros and cons. But again, it looks like historically there's been too much resistance against calendar reforms.

[1] https://en.wikipedia.org/wiki/French_Republican_calendar [2] https://en.wikipedia.org/wiki/Soviet_calendar [3] https://en.wikipedia.org/wiki/Calendar_reform