The ability to create personal caricatures on Nintendo's Mii channel was originally made for a social game released only on the DS in japan, Tomodachi [Friend] Collection.
Metroid: Other M producer, Yoshio Sakamoto, spoke at GDC 2010 about the different approaches he takes to creating games with a serious bent, as well as more comedic-based games. He revealed that an innovative interface for creating characters that his team made for the DS title, Tomodachi [Friend] Collection, was basically "stolen" by Satoru Iwata, President and CEO of Nintendo, for use on the Wii.
When Sakamoto was first shown a prototype of the character creation system that ended up being the Miis, he tried to create a character that looked like him. "Of course, I couldn't. Why can't I resize my face parts? Why can't I change the angle or location of my eyes? Don't you think that would make it look more like me?" Sakamoto asked the developer. That team member immediately went and revised the program and Sakamoto was happy to find that, with the new version, you were able to create a character with "an even stranger face than mine."
"In my usual fashion, I had to brag about this amazing discovery to Mr. Iwata. Mr. Iwata was very happy and I was the winner," Sakamoto said. "But a few days into my celebration, Mr. Iwata contacted me and said 'Can we borrow these caricatures for the Wii?' I was surprised but, of course, I agreed. Mr. Iwata also asked 'Can I borrow the team who created these caricatures?'" The room of developers laughed at the fact that Sakamoto's team was effectively coerced away from his project.
Sakamoto took a pragmatic view, though, and was happy that when his team returned a year later, they had learned a lot. And by that time, "The characters that we had created, known as Mii characters now, were spreading around the world."
That's not a bad result for what was imagined as a small feature in a DS title that was only released locally.