The screen is tipped to be "Retina display+" with a 1,704x904 resolution.
Experts also predict a faster A8 processor, better rear-facing camera - possibly with changeable lenses - and wireless charging support.
It may also include a heart rate sensor like the Samsung Galaxy S5.
It comes as plans for a new reversible USB cable were announced last week.
But now it appears that Apple is going a step further, with rumours that its Lightning cable will be reversible at both ends.
New photos that have emerged of the cable show it has a "floating" centre.
Apple tipster Sonny Dickson, based in Melbourne, Australia, has shared a photo that suggests the new Lightning Cable is completely reversible at both ends, so the frustration of jabbing at USB ports blindly to insert cables may be over.
Reversible USB port on the new Lightning cables! pic.twitter.com/bhVKjK3xKl
Just like the USB 3.1 Type-C connector, Apple's new cable will reportedly feature a reversible USB port that will plug into computers more easily, and it could be available as soon as next month.
The picture suggests that the cable has a "floating" centre, instead of pins fixed down one side, so it can be inserted into a USB port either way
Experts say that the cable will use USB 3.0 technology - an improvement on the current cable's USB 2.0.
Apple launched its Lightning cable alongside the iPhone 5 in 2012 and it was the first charging cable that could be plugged into a smartphone or tablet either way up.
It is thought that the new cables might accompany the iPhone 6, which is set to launch on September 10 local time.
A USB 3.0 cable would support HD audio, which means that Apple's earphones could be upgraded and connect through the iPhone's lightning port instead of a standard headphone jack, MacRumours reported.
Apple rolled out Lightning cable MFi specifications for headphones in June, which could mean that manufacturers are creating headphones and other devices that can connect to the iPhone 6 via its charging port.
FEATURES OF USB TYPE-C PLUG
The USB Type-C connector is a completely new design.
It has been created for use with thinner, sleeker devices, such as tablets and ultrabooks.
It claims to be robust enough for laptops and slim enough for smartphones.
It is being built on existing USB 3.1 and USB 2.0 technologies.
The plug is smaller than current laptop connectors, and more closely resembles the size of the current 2.0 Micro USB.
Crucially, it will be reversible, meaning it will work whichever way it is plugged in.
But Apple's next generation Lightning cable could be reversible at both ends.
It might also launch sooner than the Type-C.
