Sony may release a PlayStation 5 in 2020. That is what the Kotaku gaming site has heard from various sources. Details of the suspected upcoming console are still unknown and the release does not seem to be fixed yet.
If there are already devkits at gamemakers, then it will be early versions. These would take the form of a PC with an adapted motherboard, so that developers can already try out the CPU and GPU of the upcoming console and see what is possible at an early stage. Sony allows developers to install these machines in confined spaces, which few people have access to.
Little is known about a possible successor to the current generation of PlayStation consoles. The PS4 Pro came out in the fall of 2016, while the PS4 was released in 2013.