Seems like the kind of thing to do once you've already reached a market saturation point. The PS4 is only about 2.5 years into its generation.
Sony doesn't make much on hardware, especially not theoretical cutting edge PS4.5 hardware.
No, it's the kind of things when you have to deal with the following realities:
1) Games are taking longer to develop due to amount of detail, complexity, and depth of the games. A five year cycle is not conducive to the visions of ambitious developers. Last gen was seven years, and developers still had issues with transitioning. Therefore, generations must be longer.
2) Technology is rapidly advancing especially in the performance/watt arena. GPUs and CPUs are advancing rapidly in the world of PC. This is counter to the need of longer generations.
3) Virtual Reality as well as augmented reality are finally in the reachable world of possibilities. VR rendering adds an additional computational expense that taxes both the CPU and GPU.
So, what you are left with is needing a business plan that addresses the reality of needing a longer generation while also keeping pace with technology trends. Longer generations with mid-gen refreshes is thus the only thing that makes business sense in the long run.