"What if the PS4 had PS3 BC..." threads are just as annoying as the "the NX rumor" threads. First of all, I played all of the PS3 games that I wanted to and Frankly, I'm burnt out on PS3 games. I want new games to play. It's a redundant feature. The PS4 is not designed to be BC with the PS3. It's too damn late to add that feature.
My reaction if sony announced true PS3 BC for the PS4 would be to soccer kick repeatedly into the balls whoever made the decision to add it.