If you want to open an investment or foreign remittance account you need to provide your mynumber now. Existing account holders will need to provide their number by 2018. It is pretty obvious that ordinary bank accounts will be next. The government is cooking this frog slowly.
My theory is that the government is planning to pay the public debt with inheritance taxes. The demographic bump will die off over the next 25 years. Many have a lot of dosh squirreled away which the government wants to start tracking pronto. Inheritance tax ranges from 10% to 55% at the moment. I wouldn't expect it to decrease.