As long as Xbox doesn't launch a new console Sony really doesn't have to either. Hell I think Sony, MS and third parties already made agreements when to start the next gen. Releasing the PS5 in 2019 without a Xbox competitor probably means third parties are mainly going to develop for PS4 and Xone. While Sony first party studios are to busy bringing out PS4 exclusives. So that would be a barren launch which can be countered a year later by a more powerful and better supported Xbox.
The way I see it Sony would shot themselves if they abandon console that is still on track to sell 18 million units. To release ghe eauivalent of what a machine that's 33% more powerful than the Xone X for $400. When having nothing but PS4 ports ready for it by launch. The PS5 and Xbox gen 4 are going to release within 6 months of each other. Probably 2020 or 2021.
Please excuse my (probally) poor grammar
