For the most part, I've come to agree with Marcan as well. There really aren't any homebrew applications that could be made for the Wii U that couldn't also be made on, say, an Android or iOS device. That includes programs like emulators for past systems, and media players. Plus, as he said, it is a constant cat and mouse game with the console manufacturer as they try and prevent unauthorized code from running on the system. In addition, at this point in time, the vast majority of people would likely use any exploit mostly for piracy purposes (I feel pretty safe in saying that that's all the majority of GBAtemp users care about).
That being said, I still hope the Wii U eventually gets hacked, because I would like the possibility of using cheat codes on games. Plus, using Wii homebrew as an example, programs like Devolution (GameCube USB loader that runs in Wii Mode) are pretty cool, because they allow you to do things that even official Nintendo software doesn't allow you to do, like playing the Phantasy Star games online through the Wii Wi-Fi connection. Perhaps similar programs could be created that would run in Wii U mode. I don't know if any Wii U homebrew scene would ever be as popular as the Wii homebrew scene though.
Looks like that thread got derailed...
Anyway, the thread below could be interesting as well. They are working with the information that fail0verflow released on their blog awhile back, with regard to the three cores on a Wii U in Wii Mode.
http://gbatemp.net/threads/vwii-tri-core-linux.351024/