I was thinking something along the lines of an "OS" for consoles like NDS/GBA/Wii/etc.
By "OS" I mean a collection of C++ libraries that allow for universal code.
A graphics API, IO API, input API, and so forth. It could really open up new doors for homebrew dev, I think.
If not that, then writing a traditional OS sounds like fun also!
And if that's over my head, I'll probably make some web software or something. xD