For awhile I have thought banks should offer an account API. This would be a brave step for the first mover but one where I think would open a whole world of new apps and ways of looking at banking. Independent developers could come up with things the bank didn't even think of and who knows, the bank may end up buying out some of their creations? Trade Me springs to mind as a large NZ company who dragged their heels but eventually saw the light.
ASB has an API  but it's publicly published spec implies it's only usable for extracting public information from their website. 
I would assume there is something already available for the likes of Xero. But it could be so much more if opened up to other (trusted) companies. Right now, I can think of some really useful stuff I could do even if I could only access my own account.
I would be open to discussing this indepth with an appropriate person at the BNZ.