Apparently a lot of the cost and delay was making sure that the regulatory requirements for bank transfers were met. These are handled by APCA (Australian Payments Clearing Association), which is now Australian Payments Network Limited (AusPayNet)[0]. These transfers have traditionally been done over the Bulk Electronic Clearing System (BECS). BECS is a dinosaur and I have a feeling that once you achieved agreement between the members of AusPayNet (about 120 members), met all regulations, tested the new system for reliability, performance and conformance, tested the new system for interoperability with BECS, made sure it didn't have any gaping holes that allowed fraud to take place and, finally, paid some serious money to all of the consultants and 3rd parties involved in the rollout, you'd easily approach the billion dollar mark.
This project has been underway for about 6 years now. Think of it as ~$166MM per year for the rollout. I agree that it would be nice if the Australian financial sector were lean and optimized in the future, but I don't hold out that much hope to be honest, despite other countries managing to achieve this.
[0]: https://en.wikipedia.org/wiki/Australian_Payments_Network