I'm going to translate something I commented in a spanish forum about what I think Sony could do, so stay tuned for conspiracy theories that actually don't sound crazy.
Xbox made a nice movement with Xbox One X, it's not a movement which will "win the generation", not a movement which brought great joy, but a movement about simultaneous and compatible generations, mixing One with One X and also converging with Windows, in games and platform (the famous UWP). Meanwhile, Sony previously released the PS4 Pro, a better PS4 which is not as powerful as Xbox One X but anyways a competent machine, which is good to remember that still shares CPU with Xbox One X in really close performance.
If Sony is planning PS5, the best we can expect for, lets say, 2020, is a machine about a 50% more powerful than Xbox One X with a presumable price of 500 bucks, and in the meantime Xbox One X has dropped its price to 400 bucks (we can take the example, both for relative power and prices with One, PS4, PS4 Pro and Xbox One X). But... How could Sony sell PS5 in that scenario, having a little 50% extra performance from One X but three years later when PS4 had that advantage being born next to Xbox One, and only having twice the power of PS4 Pro, which also was sold just 4 years before for 400 bucks?
Here's what will happen: Sony announces that PS5 is already in user's homes. PS4 Pro could just mutate to PS5 "Core", and under this name be relaunched at the time they launch the standard PS5 at 500 bucks. This way, users will be celebrating their "free", backwards-compatible PS5s, as well as they have the option to get the most powerful console (the >8TFLOPs PS5), and Sony leaves PS4 to the memory. It's a win-win-win. Win by the price (PS4 Pro/PS5 Core 100 bucks under One X), win by the power (PS5 is more powerful than Xbox One X for 100$ bucks more), and win by the community (tons of joy for PS4 Pro owners, who also are a pre-established base of millions of consoles in the houses).
Just remember my words.