According to the technology guide Smarthouse, Microsoft and Toshiba may be working on a new Xbox "Entertainment Hub" edition. This new device could possibly add on to the current Xbox 360 specifications with a built-in HD-DVD player, HD TV tuner, and a MP3 player docking port (perhaps using the Zune docking pin setup?).
The article goes into more detail on the device and suggests that they expect it to be released late 2008 or early 2009.
News source: Smarthouse