We are half way through the 10 year expected lifespan of the 360. They don't have to bring anything announced at E3 to market within 12 months of that announcement. A 2-3 year window of development wouldn't be too far off and would allow Microsoft to one up Sony again.
BluRay, Wifi, 3D, Kinect (Natal), 1080p or perhaps even UHD, backwards compatible with Xbox and Xbox 360.
BluRay is obvious for the next Xbox with Movie support, and 3D movie support. Microsoft is definitely moving to 3D support even for the existing 360. They could use HD-DVD discs instead just to increase capacity and ignore BluRay trying to say that streaming is the future but I doubt it.