Wii Emulation and HomeBrew took a while but it happened faster then most because it was basically a GameCube. The Wii U, does not have the GameCube compatibility so Speculating on Home Brew or emulation is just that speculation. That said, The Wii-U is backwards compatible with most Wii titles that are not running off of the GameCube devkit. I am scared to think that Twilight princess might not work on a Wii U because of this fact and its one of the only Wii games I own...
sad day...
Upside, Wii controllers work on the Wii U and they Store Data that works on the Wii U for mii's This might be a back back door needed to push home brew in but remember HomeBrew Dev, and making homebrew applications with no hardware is pointless and kinda funny... If you don't know how the hardware and software runs and you can't tweak the code, how can you develop for it?
Steps to HomeBrew
1. have system and break it open!
2. Be able to debug code while system is running (on wii this was done through Gamecube memory card slots)
3. Hex edit a game while running(change values like exp, health, money, etc...)
4. Write application in edited coded information on savefile in game.
A. Before writing an application, you need to figure out how the processor runs data through the system and writes data that is compatible with how the processor operates.
(There is a reason that Mac switched to Intel kiddies! That said, Unity, has a development tool for Wii U. You might say, create what ever homebrew boot app you want in Unity? Sorry, you are not aloud to have it. Read this
http://unity3d.com/unity/multiplatform/consoles)
5. After you are able to get an application to run like Hello WOrld, Get a small small operating system to run like some distro of Linux but doesnt have to be linux mind you.... just easier people love porting it!
So if you did't read anything else.... Read this... Talking about homebrew on the Wii U is fun but pointless till some one can get there hands on a system and crack it open.