I think BC should be mandatory from now on and we should be done with single generation devices. Imo consoles should only be an entry to new possibilities in gaming and media features, not a barrier to play your old purchases or games from previous generations.
With online stores getting more and more important, we should always be able to purchase games even if they are from previous generations and I think if we can do so we should be able to just play them without having to buy them again.
Playstation had BC with PS2 and early PS3 models before they removed the feature in the later. I think Sony should find a way get get BC for PS3 games and allow previous purchases to be taken into account.