I really think someone ought to grab rabiddeity's N-Rage source and just play with it and see if they can't get it to work with Dolphin. Before he disappeared from the face of the earth, that plugin was making some good progress.
Well, N-Rage is probably too win32 API based, remember the plugins have to be cross-platform. nJoy uses the cross-platform API SDL, and right now, nJoy just needs some fixes and it should fine.