Regarding PS3, most of its games are already available on PS4, except a few gems. They could just work on those and make them available on PS4/PS5 or PS Now.
PS2 and PS1 could come back as re-released classics. They could select the most acclaimed games. Having full BC with PS2 and PS1 would benefit some players, sure, but most current gen players wouldn't give a damm. I think it'd be a waste of work. Unless we're considering plain software emulation which we know that will never happen due to many technical reasons that many don't fully understand.
God bless You.
My Total Sales prediction for PS4 by the end of 2021: 110m+
When PS4 will hit 100m consoles sold: Before Christmas 2019
There were three ravens sat on a tree / They were as blacke as they might be / The one of them said to his mate, Where shall we our breakfast take?
