Yeah, but the thing is that the PS4 emulator will probably end up running at 60fps before the PS3 emulator does, or it will follow relatively close behind. For the sole reason that the PS4 uses an AMD Kaviri chip which is x86 instead of Sony/IBM/Toshiba's custom Cell processor with its unique architecture and design. I would assume that a large amount of the compatibility issues that are seen with PS3 emulators will not necessarily hinder PS4 emulators because of that difference.
But if you have the top of the line hardware, PS4 emulation at 60fps could, in theory, be attained. But only if you had a perfectly polished emulator with few or no bugs whatsoever. I mean, because AMD's Kaviri chips are technically part of its APU lineup. So we can assume that the CPU performance is on par with that of upper tier of AMD's most recently refreshed consumer APU lineup. Next, I've seen from a number of sources that state that the graphics performance of the PS4 has been measured to a little over 1.8 TFLOPS. Which isn't bad for a console, but even at the $400 range of desktop GPUs (i.e. AMD Radeon R9 290X, which is what I own), you still get graphics performance that measure at 5.7 TFLOPS, That's almost 3x graphics performance right there, and it's a year old card. So I think in terms of raw horsepower, we could emulate PS4 games, but now it's a matter of compatibility.