Nintendo big man, Satoru Iwata has gone on record saying that he doesn't see the news that Microsoft is developing a Wiimote-like controller as a threat at all.
He also added the following, "I am also aware of the rumor and have seen a fake image made by a fan on the web which looks like a Wii Remote with the rumor that such a controller may be launched, However there is no way for us to comment on such speculations. All I can say today is, it is not that easy to develop software which leverages the characteristics of Wii Remote. We are not concerned about what other companies may do but rather more concerned with presenting them with new ideas to our customers based on the prospect that our existing customers will surely get tired of the plays enabled by Wii Remote if we do not try to improve the experience. In other words, what matters to us is whether or not we can continue to constantly create and offer new surprises one after another. If we can, then (other company’s attempt to launch Wii Remote-like controller) should not be a big threat. The efforts in this field to try to appeal to a wide variety of customers are something in which we saw potential early on and that we have been working on the longest, so there appears to be no reason whatsoever why we need to be concerned."
I guess everyone can sleep soundly now knowing that if he's not worried about it then there's no reason for anyone else to be concerned with another company stealing Nintendo's thunder.