While the CPU is indeed x86-64, the architecture of the SoC and the device is rather different so emulation still won't be all that easy.

This 33c3 talk gives a lot of fascinating information on how PS4 differs from your run-of-the-mill PC and what kind of issues they hit when trying to run Linux on it: https://www.youtube.com/watch?v=QMiubC6LdTA

It's really hard to predict that stuff. People thought original Xbox emulation would be easy, since it was "essentially a PC", but it's the only console of that generation that still doesn't have a good emulator. Meanwhile WiiU emulation is already advanced enough that it can almost play the just released Zelda:BotW.

Technology aside, it's also a matter of interest. Many XboxOne and PS4 games already have PC ports, so there is less need and interest to create emulators. Nintendo consoles on the other side have many exclusives, so interest in emulating them seems to be higher.

Only time will tell.

Yep. Both the PS4 and XBox One are using semi-custom AMD chips with 8-core CPUs and 1152 shader GPUs. So managably beefy.