Backwards compatibility is such a major feature, that games from all 5 PlayStation platforms (PS1, PS2, PSP, PS3 and PS4), will be compatible on PS5, making it an "ultimate PlayStation console", putting an emphasis on past and present gaming.
https://www.techradar.com/news/this-latest-ps5-rumor-sound-too-good-to-be-true [techradar.com]