Whilst speaking at GDC last week, Shigeru Miyamoto told MTV that the Twilight Princess team had been having some fun with Mii's.
"They've been having fun just fiddling around with Miis in the Twilight Princess engine. This is something our development teams do all the time once they get done with a game and start thinking about other ideas," he explained. It's kind of funny because you can see Miis running around in the world of Hyrule, but there's no telling that would ever actually come to fruition. It's just our team members having fun and taking off some stress after a tough development cycle."
Haha, awesome... I wonder what other games could be used to include Miis!