A planned Mad Catz Wii U peripheral indicates the Wii U GamePad headset jack will support an external microphone.
http://www.nintendoworldreport.com/news/30611
On display at the Mad Catz booth were a variety of Wii U peripherals, including a stereo headset with a built-in microphone.
While the preliminary product line on display was a collection of prototypes, the Mad Catz representative claimed that, when plugged in, the headset’s microphone would override the microphone built into the Wii U GamePad. This would mean that the Wii U controller would be compatible with the many microphone headsets on sale by various manufacturers.
This GamePad functionality would be consistent with the microphone behavior for more recent Nintendo DS models and the Nintendo 3DS, and would mean that gamers would not have to rely upon the GamePad’s more omnidirectional microphone, which could pick up undesirable noise (as seen with Wii Speak). Like on the 3DS, the Wii U GamePad headphone jack does include three conductors, which indicates microphone support.
It should be noted that the Mad Catz prototype included its own volume slider, and the Mad Catz representative was unaware of the volume slider built into the GamePad. This suggests that Mad Catz may have been designing its prototypes based on educated but possibly incorrect assumptions.
