The difficult part is to get 8 billion people to agree to pull in the same direction. And my guess is, that it will never happen, unfortunately.
I'm going to assume when this new calendar is adopted, the chinese will then be able to buy three calendars in one.
And it only "kinda" worked, because in the Chinese countryside, where most people live, 80 years later they still mainly use 农历, not the Western calender, despite all government stuff being done in Western calender dates. (I lived in China for some 6 years, just left the country yesterday, walking across the border to Vietnam).
The largest burden will be on legacy software and getting that patched. That very well could be reason enough for the reversal of this calendar, as every government software breaks, and they find out how slow they are to keeping up with their own mandates.
The difference between adapting to Y2K and adapting to the HH calendar is minor. If the gov survived Y2K they would survive the HH-adoption.