I think people are still stuck in this "mid-cycle update" logic (although I agree to a lot yurinka said). Meaning that the inevitable successor of PS4k / Neo will be PS5 at some point, with a very own library of games. From my point of view, this iterative console model means something else. I tried to visualize how I see Sony's roadmap for the future (sorry that doesn't look more sophisticated as I created this with vanilla PowerPoint at home):
So, basically, two SKUs together establish one "generation".
Each generation is defined by the same library of games. So devs are forced to support two SKUs at the same time (it's up to them to support older SKUs as well).
At the same time, in this model Sony only supports two SKUs at the same time (like Apple does with their iPad if you ignore the different screens sizes).
If this model applies, there won't be a classic "PS5". Or a "next generation" as we are used to. Instead, we will see incremental updates and a shift of supported games with each new SKU. Of course, that doesn't mean Sony cannot name Neo successor "Trinity" PS5.