For the most part, hacking groups discover possible exploits for systems almost immediately but it takes time to create a viable exploit from these. I imagine that one of the reason's Nintendo forces the Wii U to reboot into a Wii emulator to play Wii games is to act as a "quarantine" to protect the Wii U from possible Wii security holes.
While I could be wrong, I expect that the Wii homebrew exploit will fall far short of running software on the Wii U; but it could be helpful for hackers to learn more about the system.







