It is not x86. x86 is 32bit architecture. The PS4 is a x86-64 architecture which is 64bit (even better than 32)
To be honest with you, I think it will come back due to the PC 64bit architecture. Same with PS3, I could seriously see Sony bringing it back to PS3 once they stop updating the console.
Nope. Just because their is a USR folder and an .elf file doesn't mean anything. Its true that the PS3 and PS4 run a custom Linux Kernel, but anything can be named USR for many purposes. Hell, I could change the folder name to SUPERDUPERSYSTEMFILES with superduperelffy.elf if I wanted to.
But yeah, it does have Linux kernel and I could see the other os feature coming back.