NFC: There are many phones that already use NFC right now, and Apple should just as well catch up. Probable clues: Passbook app is a Google Wallet equivalent that might need NFC for a full-fledge experience.
4G LTE: 4G is key if Apple wants to reclaim it’s stake from Android. Probable clues: Apple has made features that would be in the next iPhone in the iPad, such as the A5 chip. 4G is the next new addition to the newest iPad, so LTE should be in the next gen iPhone.
A5x or A6 chip: The new A5x chip with quad-core graphics power is faster and more powerful, but some people still demand more such as quad-core processing. Probable clues: The A5 chip in the iPad 2 showed up in the iPhone 4S, and at least an A5x chip should be in the next-gen iPhone, or whatever it’s called.
iOS 6: I would faint if Apple didn’t include this in the next-gen iPhone. Probable clues: Do you still need any?
Better camera: There should be a bump up to 12 Megapixels or better wide-angle lens, an optical zoom or even interchangable lenses! Probable clues: Apple recently filed a patent for interchangeable lens and Apple likes to keep improving it’s camera.