Now I'm not saying it's easy or even possible, in fact I would peg the honest chances of a superior time system being adopted at 0%. The cultural inertia and business costs associated with the change would be practically insurmountable. But the ease of use improvements one can make on the calendar are spectacular, such that if the change were ever possible, the business costs saved, and the mental improvements in how time is metered and calculated and planned out for the average Joe, would be vast.
In decimalizing time, the Chinese did it along time ago, and the French even tried it once (although these systems mostly had to do with dividing up a day, not a year). So here we have just an intellectual exercise, inspired by a thread involving mostly delirium and myself.

The most important bedrock issue is that 365 days in a year is a hard unchanging fact of the solar calendar, and must be worked with. Not much to do with base 10 there.

**Ten months of 36 days (or alternating 37 days)**

To decimalize that then, there should be 10 months of alternating 36 and 37 day months: 365 days total. Or perhaps ten 36 day months, and a 5 day "special" week at the end of the year. The special week could be all holiday, or a 4 day work week with only 1 day off at the end of the week instead of 2. The leap day every 4 years should always be tacked onto the end of the year as a special holiday day off.

Each 36 day month could be comprised of six 6 day weeks. the work week would be 4 days, instead of 5, and you would still have 2 days off from work at the end of the week. Or, with a 36/37 day alternating month model, the extra last day of every other month could be a "special" holiday day off.

The biggest plus of this system right off the bat is the most important bonus: the normalization and synchronization of years, months, and weeks:

- The beginning of the year and the beginning of the week always coincide

- The beginning of the month and the beginning of the week also always coincide

- Months always have the same number of days (unless you are with the 36/37 day model, in which case, they are uniform in their simple variation of every other month)

Another bonus of using a 36 day month is that certain subdivisions of the year still remain possible that a 12 month year allowed: thirds and fourths. 10 months of 6 weeks means you have 60 weeks in a year to play with and divide into seasons or business quarters or even thirds, as you wish. The seasons would merely fall midmonth here and there, as they already do now in the Gregorian Calendar anyways.
A 6 day week, with only 4 week days, means that only 2/3 of a year is spent at work. This is an improvement in the concept of how much work should be expected in society, a concept of less work for all that has been advanced in the West as it moved into, and out of, the industrial era. This has culminated in a rich number of vacation weeks in Germany (4) and France (5!) and Denmark (6!!), but not yet realized in the USA, still stuck in a Victorian mode of thinking about how much time should be spent at work.

Now, if the 10 months of 36 days model is considered, and if the work week begins on Monday, January 1st every year, then the last workday of the year is now always what is now December 24th. How do i get at that?: with ten 36 day months, you have one 5 day special holiday week of leftover days, which would run from what is now December 27th to December 31st. And therefore the Saturday and Sunday of the last 6 day work week would be the 25th and the 26th. What's the point of making this observation? Well, in the Christian world, this would mean that the special holiday extra long vacation week at the end of the year would always start on the religion's most important holiday. That's just a bonus for getting support for this decimal calendar: the Vatican would love it.

**Ten months of 35 days (plus a half month)**

However, bringing up religion brings up a huge obstacle, perhaps more insurmountable than business or cultural considerations. Sunday, or Saturday, or Friday even, are considered holy days. Messing with the 7 day week then is basically picking a holy fight with the entire branch of Abrahamic religions.

So, if the attachment to the 7 day work week is so strong (which it would be also from the headquarters of industry, who might not like their workers going from 5/7 (71%) of the year working down to 4/6 (66%), even if the switch was mandatory for their competitors too) then it is however still possible to decimalize the year and retain the 7 day work week. Just go to 10 months of 35 days instead, each month comprising 5 weeks of 7 day weeks.

This would leave a special 15 day period at the end of the year. That could be composed of two 7 day weeks, and a bonus holiday day. A sort of half month at the end of the year. That's a disadvantage, and ugly. Additionally, the disadvantage of this system is now you have a 52 week year (plus 1 day at the end, or 2 days at the end during leap years). Now unless your attachment to a deck of playing cards is very great, 52 is obviously inferior to a 60 week year, and the divisional superiority of that number.

However, retaining the 7 day week does make transitioning from the old Gregorian Calendar system of dividing the year to the new system the least psychologically, culturally, religiously, and economically painful. All one would have to do, assuming enough governments agreed to the superiority of the system, is plan ahead (for software code updates, for example), and pick some year in the future, 10 or 15 years hence, where Monday and January 1st just happen to coincide.

This day would be the first year of the new system. By making the transition this way, the procession of weekdays would remain completely unchanged. Next, simply drop two "unpopular" months, say February and November, and leave the other 10 months unchanged in name and sequence. Merely give them 4 or 5 extra days, so they would all be 35 day months uniformly. The special half month period at the end of the year could be a special religious holiday season. This would ensure the support of the Abrahamic religions and the average Joe (if not the business community).

**Decimalization, Schmecimalization**

Delirium brings up a good point: there really is nothing much decimal about these proposals. In fact it is the uniformity: the meeting of the years, months, and weeks in a regular simple pattern, that is most important here. In fact, if there were 7 months in the year, or 20 months in the year, or whatever, it doesn't matter: it would still be superior to the current system if it introduces harmonization between the weeks, months, and years.

So say we keep 12 months in the year, and normalize all months to 30 days, or 5 weeks of 6 day weeks. This proposal would need a bonus 5 day week tacked onto the end of the year. Or, to preserve the 7 day week structure, have 13 months of four 7 day weeks, for a total of 28 days per month. This system would need just 1 day tacked onto the end of the year during nonleap years.

Now please don't say that the chance of these vastly superior ways of organizing the year has zero percent chance of being adopted. That's obvious. This story is just an intellectual exercise, a fantasy. But of course you can appreciate the superiority of these more uniform hypothetical time systems, and that is my only motivation here: an interesting intellectual exercise, no more.