Perhaps the real reason why Apple put 64 bit on the iPhone 5 S…
What if the real reason why Apple put 64 bit on the "forward thinking iPhone 5 S ", is simply because they are in the process of building a laptop or hybrid device that runs a "pro" version of iOS. A 64-bit version of iOS that's designed for a laptop or some sort of new laptop tablet type hybrid with a 13 or 15inch screen.
The iPhone is merely a Trojan horse to get developers to start writing the 64 bit apps. Once this device is ready, Apple can simply say that it runs all of your mobile 64-bit apps that developers have been developing for the past year!
I can see a device like this having more than 4 GB of RAM, and needing a 64-bit architecture just like any other desktop or laptop. The only difference is that it would run iOS instead of OS X, presumably Apple will begin to fade out.
I have a feeling that this is just one small piece of the puzzle, and we can't see the big picture but Apple has some sort of plan.