IGN Has just updated this article with Microsoft's Response:
Microsoft just got back to us to clarify the Xbox 360's ability to transmit a digital signal. In short, it can, which means that Microsoft could conceivably release an HDMI cable for the Xbox 360. This is good news, and relieves a great deal of our concern over the Xbox 360's ability to effectively work with 1080p. Microsoft's full response is marked in the Q & A portion of this feature.
With this new information in mind, consider us relatively mollified. A future HDMI cable for the 360 will resolve the problems we outline in our discussion of 1080p compatibility. Let's hope Microsoft decides the market demands it sooner rather than later.