Each generation has been exponentially more challenging to emulate than the previous, so don’t hold your breath for reliable PS5 emulation.
Not really. PS4 is easier to emulate than PS3, if you are on x86 PC hardware. The development just didn't have as much time as PS3 yet, but its not exponentially more challenging than PS3. PS5 is basically a PC, so emulating games wouldn't be THAT hard. Like with PS4, they don't need to emulate everything of the CPU (if you are playing on PC).