The rumor now is that Microsoft is figuring out a way to make the next XBOX forward compatible with all old xbox 360 games. The games will have improved graphics, more speed, and the buttons will be rearranged on the controller.
Microsoft is still "testing" the functionality of this new feature to makes sure everything works before coming up with concrete plans. The next XBOX isn't supposed to be released for another couple of years so this news is purely hypothetical.