Games are probably going to become multicore, PS4 or not. Having a
multi-core console might accelerate the process, adding incentive, but the PS3 and Xbox 360 were both multicore before; the only difference is that now they are x64, rather than PowerPC based.
And why would the FX series particulary benefit? The PS4 uses Jaguar not FX cores.. At any rate any optimizations made to the PS4's architecture would most likely be properietary to Sony.