It's a pretty simple change.
All the Wii code does to reset is set the first bit to 0 in a register at memory address 0x0d800194.
This doesn't quite do the trick on Wii U but there's another register at memory address 0x0d8005e0 that can also be used to reset the console.
You do the same thing to that register, set the lowest bit to 0, and it will reset the console on both Wii and Wii U
In the code, basically all you do is replace 0x0d800194 with 0x0d8005e0 and you're done
and no, it is no more exploitable than it is to just hit the power button to turn on the console when you first plug it in.
Okay cool, I'll give it a shot when I have the chance!