It probably has more to do with the overall environment of the console, I.E. software, integration with Windows 8 and the tablet/phone versions and the user experience than it will be the outright performance of the system. Given we're looking at an 8 year gap between the systems I suspect what we'll see will be based on the Xbox 360 S type design parameters instead of the original so I suspect a profitable system with decent performance and a focus on accessories will be the order of the day.
Tease.