I'm not sure they were promised a 100 year ruling I think they were promised (if they were promised anything) confidentiality. If so to release the records at all could be considered breaking the 'promise' of confidentiality, which is why I believe the Australian censuses were actually destroyed. Since I would rather see a census after a 100 years than earlier when some people still living might chose to contest its release, or people in the future might consider contesting further releases on the same grounds, I would prefer patience to the possibility of no census at all. I think the view is you cannot expect people to fill in future censuses if they think the release of the information will get earlier and earlier, as in the United States where the 1930 census has been available for some years.
Regards
Valda