Apple's 30-pin connector is more or less hitting its limit (e.g., no digital audio/video output). It's possible that Apple maybe looking at Thunderbolt to replace it. Faster syncing, ability to output audio/video to monitors and TVs (via HDMI adapter)... why not?
As for the microphone, it doesn't need a big opening.
With Verizon (and soon AT&T) offering WiFi hotspot capability with iPhone, I am hoping WiFi iPad 2 will gain GPS.