Both the Xbox One and the PS4 will lack backwards compatibility for their predecessors. The architecture for this generation of consoles is simply too different to emulate previous generations.
One of the big missing features from both the PS4 and Xbox One out the box is backwards compatibility. The next generation hardware arriving later this month is simply too different in terms of architecture to attempt including backwards compatibility as a core feature. And while Sony is promising to offer the ability to play older games next year through Gaikai, Microsoft isn’t for now, and probably won’t for this generation of hardware.