XOne probably will last that long, because it's highly doubtful that there will be XTwo. Minor hardware changes have been announced today for their entire devices division, with more pronounced focus on pushing "digital life experiences".
I expect that the future will see more focus on mobile (their core business), with continued investments into Windows Phones and tablets, in order to increase market share in growth sectors.
Halo: Spartan Assault 2 might become more important to them than Halo 6 in a few years.