According to President Andrew House, Sony was never going to block used games or implement any kind of DRM in the PS4. See the full quote below.
“Dating from about our February event, there had been questions about what our online policy would be. I have to say that we were slightly perplexed, because we had no intention of changing from a model that I think has served us really well for several platform life-cycles.”
“We’re a game publisher ourselves, so there’s a certain argument for us that there should be something of a model for content-creators to participate in second sales. Having said that, however, the consumer sees ownership as a very key benefit when purchasing a physical product. And the flipside of the argument is that retailers will tell you that the vast majority of trade-in value gets immediately repurposed into new purchases of games, and those people in turn generate word of mouth and create more interest.”