A new patent for "backward compatibility through analog clock frequency and fine-grained frequency control" appeared on the U.S. Patent and Trademark Office website that was applied for by SIE and invented by PS5 chief architect Mark Cerny and others. The patent first appeared in 2017, but last week Sony updated it with a lot of content.
One of the descriptions of the patent mentions that the patent is for systems that are weaker than the current system, and that backward compatibility is achieved in the form of software.
In the Bloomberg rumor about Sony's new subscription to "Spartacus", it is mentioned that the highest level of subscription service will provide classic PS1, PS2, PS3, PSP game libraries.