Stupid shameless guesses here:
a) 3d screen (adjustable like Nintendo 3ds)
a) 2 front cameras to record 3d for 3d facetime
or
b) Ultra hi-def screen 2048 x 1536
quad cpu that is actually also gpu
power cpu with clock speed throttling (to control power consumption)
a total redesign of iOS but has compatibility mode for iphone/ipad1 apps
*dont kill the golden goose
fm transmitter so car stereo integration doesnt need special cables or anything
hdmi output with audio