Sony still not pursuing backwards compatible for PS4.

[Baryonyx]

Backward compatibility on the Ps4 would require a Emulator and Emulators alone requires more then 4 cores and then there are basically no power left for the Ps3 games to be able to run great or good on the Ps4 and we would be better off with the ps3.. There is a reason why we don't have a Ps3 emulator on PC yet including the fact as the PC get stronger it might achieve that goal, but the Ps4 will stay the same. 
I am not exactly sure how many cores it requires to run a Emulator, but i remember reading something in the line of 4 cores for a DS Emulator