I'd have to agree and disagree.
I agree with what you said about MM being mature.
What I disagree about is your def of mature. Mature could be a wide variety of things and calling anything "mature" might be childish in someone elses eyes.
Everyone is still going to buy it. People didnt buy TP for the Gamecube only because it was ported onto the Wii. Since this isnt getting ported, and there is a lot more time between releases, every true Nintendo fan is going to pick it up.
I would love to keep my hopes up, but I dont think he will actually be in the game at all. We might get a few references to a child being born or something like that. I also at the end their will be a big scene where he is born, like Link is too late or something.