Possible backward compatibility PS1, PS2, PS3 with PS5 in the future
While most games for PS4 can be played on PS5, it can touch an old sensitive point. Previously, games for PlayStation 1, 2 and 3 could not be read on PS4 due to compatibility issues. Previously, all PlayStation system games could be played on the previous consoles. Although some games have been removal since and can play on more recent consoles, it does not apply to all games.
But, it may not be a problem. A Twitter user was able to find a Sony certificate that had a backward compatibility in his title. To be precise, the name of the patent is: downward compatibility thanks to the use of a falsified clock and a fine-grained frequency control. This means that this patent could be an application on the PlayStation 5 that could be used, so other applications on a different standard frequency clock could work.
In short, it means that games that work on less powerful consoles (like the first generation of PlayStation) could be played on the PlayStation 5. It means... Maybe we can play our old PlayStation games again.
However, this can mean that this only concerns PlayStation Classic games because it is a software and non-material fix. This means that even if we can play classic PlayStation games, this can be limited to what can be found through the PlayStation — PlayStation Plus or PlayStation Now subscription service, otherwise a later combined application of both.
This has not been confirmed by Sony yet. Thus, there is currently no exit date on any descending compatibility, and this may be more than just software. And I hope if it comes in the form of a subscription service like the Nintendo Switch extension... I hope there has been some care to make the games we know and love more playable.