Sony offers new insight into PS5 compatibility
Firstly, DualShock 4 - a.k.a. the PS4 controller - can't be used on any upcoming PS5 games, with Sony stating that it wants the new titles "take advantage of the new capabilities and features we’re bringing to the platform, including the features of DualSense wireless controller."
However, the new post on the PlayStation Blog does confirm that DualShock 4 will still be able to run on the new console when playing PS4 games via PS5 backwards compatibility, in addition to third-party gamepad controllers for the PS4.
Makes sense really.. You'd want the ps5 games to solely use the new game pads features