As I said, I think it is precipitous for anyone to be considering 64-bit mobile devices at this stage. Even most PCs barely make use of the technology.
64-bit by its very nature requires more power, more RAM, more processing speed and apps are larger in size. All these things create issues for current mobile technology. It's not there yet.
Apple has implemented a very limited 64-bit system, aside from a minor performance boost which comes with 64-bit being more efficient at certain tasks, there aren't many benefits at this stage.