I don't understand the logic of even contemplating not upgrading to USB 3.0. It makes no sense to me to stay at USB 2.0 when 3.0 is already on the chip.
But will the use of Retina Display lead to overheating, shortening of battery life? the original display is good enough for me. I would like to see improved processing power and a 15 inch version
No that will not happen, if you look at iOS SDK - it will explain why. Something dealing with screen resolution and power of 2. One thing that might be possible is larger device. 19 by 14.6 in device with 4096x3072 screen.