The big jump is going to come from the CPU, Jaguar was crap when the PS4 launched, Pro/Scorpio are still using that under powered CPU.
I think PS5 will likely be 10-12TF, have 16gb/24gb of ram, modern CPU architecture. I could see this device launching for $399 holiday 2019, maybe selling for a slight loss.
That new CPU is going to do wonders.