I would think they are definitely looking at 2018 internally to see if that's feasible. 5 years on the market is historically normal but after last gen's lengthy lifespan, I wonder what the market would think about 5 years. 4 years is out of the question and it's not as if Xbone is in the same position as Xbox 1 was. Lots of money to be made in that Year 5 but they do need to weigh a Year 6 against getting a head start on Gen 9.