One part of the rumor suggests that the iP 5 will replace the iP 4 across the board. According to the rumor, it will have a Cortex 9 based processor and a number of other improvements, probably including an updated antenna design. One rumor suggested that there will be a metal, not glass, back plate and that it will be a backplane antenna design. All rumor, but the processor part would explain why Apple used the Cortex 8 processor for the iP 4...they simply did not have the Cortex 9 based processor ready at the time. This goes along with the iPad update rumors that include a processor update, more RAM to bring it up to the iPhone spec along with a Retina display & yada, yada, yada.
I think that Apple probably has concluded that the overall size of the iP4 is smaller than it needs to be (it is actually difficult to handle because it is so small) and it restricts screen size, battery size and a host of other possibilities. Please put a micro-SD card tray, like the micro-SIM card tray in it, Steve! HDMI output and micro-USB 3 would be nice, too.