My interpretation from all the info we have, is that Sony planned for 2019 years ago. But then delays in certain elements mean they pushed it to 2020. However, parts that WERE ready for 2019, still are ready for 2019.
The polishing of PS4 BC feature makes sense. if Sony really want it to be a big deal at launch, they need it to be seamless. Remember, even XB1 BC of 360 games isn't actually seamless, it was still done in a per game basis. A big part of PS4 BC would be to get the PSN network updated, which we know they are working on. If it was just about getting PS4 discs to work on PS5 it would certainly be an easy thing to implement. But too many parts of modern games have download and online elements today, and PSN itself is archaic.
The polishing of PS4 BC feature makes sense. if Sony really want it to be a big deal at launch, they need it to be seamless. Remember, even XB1 BC of 360 games isn't actually seamless, it was still done in a per game basis. A big part of PS4 BC would be to get the PSN network updated, which we know they are working on. If it was just about getting PS4 discs to work on PS5 it would certainly be an easy thing to implement. But too many parts of modern games have download and online elements today, and PSN itself is archaic.