Anyway, I'm rambling now. To get back to your question in the OP - I'm not sure whether Nintendo should do it (and I'm not sure if they ever will), but it would certainly be very interesting to see. Nintendo are obviously very, very good at what they do - and they make sure what they put out is more polished to a fine tip. But a bit more diversity wouldn't hurt - trying something new wouldn't necessarily be a bad idea.
Some divergence from a formula that for me, at least, has become too formulaic, too predictable is exactly what I want. I've heard people say Nintendo should just keep doing what they do best as long as it proves successful, but I'd love them to take a "risk" with a new IP from one of their major internal studios. I say "risk" because what real risk is it? They're in such a great position right now; they have no shortage of money, it's the launch of a new console aiming for the core market... if they really believe in the studios they have, surely they trust them with simply doing something else? They're sitting on the next Zelda or Metroid right now.