Microsoft also considers the creation of an open standard docking port for MP3 players, so the support can be much broader than Zune:

From SmatHouse : 

The new Xbox device, while allowing for extensive gaming capability, will be positioned as an entertainment hub that includes gaming and extensive wireless networking capability as well as 1080p playback. There is also talk of it including a dual HD TV tuner and EPG capability and a docking port for an MP3 player. For Toshiba, the device is critical if it is to be successful in beating Sony and the Blu-ray promoters.

Also being discussed is the development of an open standard docking port similar to the 17 pin iPod port. This would allow all manufacturers to use the same port for docking.

The entertainment hub concept Microsoft is thinking sooner or later will have to include Zune. Considering this Wireless Networking now that Zune 2 will Wirelessly sync with PCs, with a Zune Software and Marketplace support on Xbox, things can get pretty interesting.

This new Xbox model is expected in 1 year, late 2008 or early 2009, so we can start talking about possible Zune 3 features from now on.