We're going to need something a lot more heat resistant than silicon if you want an Octo-core @2.5Ghz per core processor in such a thin space. In a heavy usage scenario the system on a chip would fry itself very rapidly.
Built in stereo eye tracker so the phone knows where you are looking, with the possibility of using blinks or sustained gaze fixation to select buttons.
Larger screen that creates 3-D effect through parallax motion using the eye monitoring from above.
Solar or kinetic charging integral to the phone - no more issues about batteries except when they wear out.
Self-healing (up to a point) nano-material exterior
Intrinsic language parsing (Siri, but without the need for network access)
Graphic development environment that allows mere mortals to create apps for the Mac, iPhone/iPod, and iPad without having to learn arcane, counter-intuitive programming languages
The ability to control not only TV's, multimedia centres, but iAppliance interfaces that Apple is beginning to create to dominate the home & automobile automation market (presumably based on Apple protocols and/or chips that manufacturers can use to control heating systems, cars, ovens, phones security systems, etc...)
Bulletproof anti-theft hardware and software
min 128 GB memory
No *&*^%$^&& mechanical home button. Instead, there will be a touch-sensitive Apple logo with no moving parts.