Depending on how the emulation is done PS4 might have a slightly easier time. AFAICT from some time ago i checked it, PS3 is probably the hardest architecture of all to emulate with RPCS3 basically using LLVM to "compile" code fragments from PS3's CPU to native code.

I'd expect running x86 code written to run on an AMD APU with a Unix-based OS in another AMD APU with a Unix-based OS to be a bit easier, probably with some VM involved (even Xemu, the original Xbox emulator, is basically a QEMU PC configuration with some Xbox-specific hardware for the GPU and audio).