Kotaku supposedly has some credible information about the XBox360.
Changeable covers would be excellent. The wireless pads are probably done via Bluetooth, so hopefully there will be built in Bluetooth system-link too. I don't know why Microsoft would still be having problems with backwards compatibility, but the XBox360 will suffer if it doesn't have it. Positively however Microsoft could offer such functionality as a free download over Live, thus leveraging more people to signup.