I've got to say it could go either way!
We know on a global scale Nintendo is well know to parents who grew up playing the Nintendo games. These parents do what - Buy the consoles for their children and trust in Nintendo's brand quality. Infact Nintendo is so well known for its family friendly software that almost anything provokes a public outcry. Remember when CNN reported a gil was talked to by a stranger who asked hesome personal things over DS Pictochat he had to have been within feet of her yet their was a public outcry. The Wii launches the Opera browser and right aways a group of angry Christian Parent's boycott Wii claiming it is a Portal of Porn when their are child locks and Wii can't even play .Mov or any other media files except Flash. Infact the kid would have to accidentaly come across a porn site that just happened to be entirely in Flash and accidently enter his age as 18 or older and then accidently click on a clip. The amount of accidents that would have to take place is amazin. Yet parents were outraged that it was even possible, all it takes is a parent to actually watch where their kids are online!
We know theirs bound to be a huge backlash of families abandoning Wii but is it financially viable for them too? A family buying a console for their kids isn't always gonna want to dish out 699CDN or 499CDN for a single console. The option of 279CDN for a console and games is far more appealing. Low/Medium income households will be pushed towards Wii regardless of their moral objections this could give Nintendo a grace period where they can get away with M games without damaging their user base too much. Keeping damages minimal theirs a chance M games could benefit!
Right now Nintendo is known for family friendly entertainment. However the inclusion of numerous M rated titles could boost its support of the older age demographics such as 20-35 year old males as well as the gore crazy teenagers. That can help Nintendo largely in the short term with millions of units possibly sold because of the inclusion of such titles. It also makes the console more for everyone and gives adults something to play when their kids are out this could benefit Nintendo in less conservative countries or (States/Provinces)!
In the end its a question of short term gains (M titles) over long term losses (Family user base)!