The rumor comes our way from the folks over at The Verge who previously brought us the rumor about the $99 Xbox 360 subscription plan (so that's gotta earn them some clout.)
According to their source, Microsoft is currently working to implement IE9 functionality into Xbox Live and will be adding Kinect controls as well. That means voice and motion control in your web browser. Which is probably useful for somebody. Maybe.
This will expand Xbox Live internet capabilities by offering full web browsing without having to use a smartphone, laptop, or getting up off the couch to use a desktop PC (the horror.)
The source did not give an expected release date for the implementation of this service, but as with all rumors these days, it's unlikely we'll have to wait too long for confirmation. E3 is right on the horizon, and if the rumors are true, that's the place it will come to light.
And for everything on that, our E3 rumors compendium page has you covered. For everything.