The big problem with this is that in order to debug and reverse engineer it, you need a physical connection to the Wii U's motherboard, because any software you run to send debugging information over the network is flushed when the system reboots into the modified vWii mode.
Hey, Nintendo, maybe one of the big reasons for the Wii U's commercial failure (besides abysmal marketing) was your refusal to do simple things to allow the consumer to easily tap more of the device's full potential? Such as a settings menu you can open on the GamePad in vWii (maybe using the TV Remote interface?) that would let you "plug" the GamePad into one of the four Bluetooth ports as a Classic Controller or Wii Remote Plus (using the touch screen to emulate pointer controls - it wouldn't be perfect, but it'd be worth a try)
Of course, asking homebrew devs to do all that is stupid. They're having a hard enough time getting the basic support working. But Nintendo could have done it. They have the source code, and the signing keys for both the Wii U's OS and the GamePad's too.