Pokémon Bank was supposed to be available in Australia on the 28th of December 2013 but due to certain circumstances the release date in Australia will probably be post-poned for a later date.
This is because Nintendo are currently experiencing technical difficulties, as a result of this the Nintendo eShop is under maintenance.
You can check the current network status of Nintendo at this website:
The reason the Nintendo Services are under maintenance and currently unavailable is actually due to the release of Pokémon Bank in Asia. As a result of this Pokémon Bank has been temporally removed from the Nintendo eShop pending an investigation.
Therefore locations where Pokémon Bank was to be released on the 27th of December 2013 (North America and Europe) and on the 28th of December 2013 (Australia) are currently listed with a release date of TBD (To Be Decided).
No it is not it should be available December 27th (tomorrow :D) to every where else it wasn't released. I can't remember which countries got it on Christmas but most of it was Asia.
Edit: Pokebanks's released date will be pushed back due to a server error people were having. (I also did say should :P)
Read more here: http://www.polygon.com/2013/12/26/5244942/pokemon-bank-taken-down-in-japan-following-server-issues