Apple could be planning on making the move to 64 bit processors with the iPhone 5S and new iPad. Very basically speaking, the change would allow the apps and OS to use more memory, and therefore run faster. Animations, like those introduced in iOS 7, could be more complex and more smooth. 64 bit processors can run 32 bit apps, so developers wouldn't have to do much, although they may wish to tweak some of their code and recompile for 64 bit processors. Basically, it's a move that wouldn't require much work from developers, but would make iOS faster.
Finally, details are starting to emerge on the processor that will power future iOS devices.
According to Clayton Morris, a reporter at Fox News, Apple's new A7 processor will be about 31% faster than the current A6 processors. The processors are rumored to still be dual core, but may be more efficient, or run at a faster clock speed. Analyst Ming-Chi Kuo claims that if the A7 processor doesn't use 64 bit, the A8 will, as Apple is currently testing 64 bit processors in iPhone 5 casings. He has also reported that Apple will use faster memory with the new processor. A move to 64 bit could explain some of the performance boost that Morris had reported.
According to Apple, the "S" in an iPhone name stands for "speed". The first of such "S" models was the iPhone 3GS, and it was the first to start the trend of improving the speed, efficiency, and other features of the iPhone without changing the external design. The iPhone 5S is expected to continue this trend, with a faster processor, improved battery, better camera, and possibly a fingerprint scanner and NFC. Apple may also begin offering the iPhone with 128 GB of storage space, especially if a 64 bit processor is introduced, as 64 bit apps tend to be larger than their 32 bit counterparts.
Source: 9to5Mac