If I'm not mistaken, it's up to the dev to include custom soundtrack on PS3. And I'm pretty sure they patched it for SSHD but I never used it. The original soundtrack is too important haha.. keeps me focused and after 300+ hours, I'm still not tired of it
Personally, custom soundtracks are good for racers but for everything else, I prefer the original soundtrack. I'd bet it's integrated in the PS4 though.. it has to be if Sony truly listened to what gamers wanted.