Iwata recently discussed a variety of issues, including the company's policy for licensing Miis to third parties.
For multiplayer games, it's been strange that Miis haven't made a great deal of appearances and have only been seen in a select few titles in the Wii's catalogue. As well as chatting about the Wii's storage issues, the big Nintendo boss was also questioned on licensing Mii content to third parties.
To Nintendo, licensing Mii is identical to licensing Mario. If you read Iwata Asks interview series in website, you can understand how Mii was created in detail, so I hope you can read them if you have time. Mii is actually the result of more than 10 years of efforts.Mr. Miyamoto, the inventor of Mii, himself has been saying that, "In a sense, licensing Mii is same as licensing Mario - Nintendo should grant the license when we can conclude that the proposed project is worthwhile. Should we allow any and all the licensees to use Mii license for whichever projects, Mii's brand image will be hurt. Because we are not granting Mario license to any and all, we should not do so with Mii either."
This is the current policy of Nintendo. So, at the software development stage, we are consulting with the developers as to how they would like to make use of Mii, and our Licensing Department handles on a case-by-case basis.
Essentially, the company don't want others using Miis and ruining the image Nintendo have built surrounding the interactive avatars - so chances of seeing the option to slash off Mii heads or engage in sexual acts would be fairly low.
Thanks to Siliconera.