I think at issue on the banker's side isn't his opinion on bitcoins as much as alternate methods of cheap cross border money transfers.  Can't say I know much about NZ, but Australia has been a leader in low cost FX transfers with such companies as OzForex and Technocash (their target audience are small to medium export/import businesses transferring funds between subsidiaries, vendors, and suppliers).  As NZ has a commodity and tourist based economy, I can only assume they have similar needs to Australia.  Therefore, if a banker from that area is talking bitcoins, it more than just digital currencies, but part of a strategy to maintain their market share on cross-border payments. 

Theoretically, for a bank driven product, something like XRB which is credit based would make the most sense.  A bank could help a firm issue XRB that is backed by their earnings with the currency being tradable between suppliers and buyers and transferable at the issuing bank.  On this point is why a NZ bank, or any other one for that matter would be interested in a digital currency as they could offer reduced rates to the debt issuer, while still controlling the entire loop of commerce.  So, it would be centralized, but via the financial health of the bank or company selling debt.  its actually not much different from the debt offerings used in the shipping industry during the 1500's or so. 

I'll make a prediction here, if a few banks can pull something like this off, IE a digital based debt offering, we'll quickly see the Goldman's of the world jump in, and ultimately create another financial crisis like in 2008 where everybody was borrowing against each other and when a few companies failed, the house of cards fell down.  (Gary V likes to say 'marketers screw up everything', can probably interchange 'bankers' with marketers) But, we are definitely still many years before seeing something like this take place