You can't react that fast in the hardware arena, and you need software on your hardware to make it sell.
Whatever timetable both are already set on for release it won't change unless the hardware isn't ready in time (PS3) or the games aren't.
The idea that Sony will move up production because of Scorpio or delay production because the PS4 is selling well is madness. We already know how long it takes to make these games, fabrication of chips has to be done well in advance etc etc.
They like a November ish launch because it rapidly expands userbase and gets lots of christmas headlines. They aren't going to have it booked in for November 2019 only to go "oh its ok lads, lol Scorpio so just hold off for now and well do it next year".
On the basis that I think Scorpio is still a Jaguar with a bigger GPU, the PS5 in say 2019 is going to be a substantial leap in CPU and GPU power over it as it'll be on Zen or whatever. So for me the question isn't really what Sony will do for the PS5. It almost looks obvious by comparison to what MS will do.
If Scorpio does come out this year and is Jaguar with more GPU, are they then also going to push for a Xbox One Two or whatever in 2019 to go with the new CPU and whatever GPU bonus's come, or are they going to wait a year and let the PS5 be the only kid in the playground with a truly next gen system for 12 months. For a brand that's only really strong in NA and the UK, waiting a year isn't exactly going to help. On the flip side, Launching 2 new machines in 2 years isn't going to sit well either.
All of this is of course out the window if somehow despite everything MS have put Zen in the Scorpio.