Absolutely no way that we hear nothing about the PS5 until 2021 or 2022. If they want to go with a 5-6 year console cycle we're looking at 2018-2019 launch. Meaning not out of the question we hear something this year or by E3 2018. The Pro is not selling like crazy and certainly not generating enough interest and sales to say that it can extend the PS4 life cycle by maybe more than 1 to 2 years. Sony is vague about numbers, and instead makes comments like this "The sales of Pro are stronger than that of Slim, as we see it. - (CFO Kenichiro Yoshida during investors call for 3rd quarter earnings ending December 31 - 2016). If it was selling well they would be waving a giant flag with the big number on it, the fact that they aren't tells us everything we need to know.
If we go with a 6-7 year life cycle instead due to the Pro, it still launches in 2020, probably revealed in 2018 or 2019.
These "mid gen refreshes" are going to be interesting in how they effect the consoles life cycle, if much at all. I'm a big fan of both MS and Sony and have always owned both consoles. Please don't take anything above as being some sort of console war crap, it's just my thoughts around the business decisions and financials of launching the next systems, etc.