They are probably targeting 16 gb with 8 gb reserved for the OS
Knowing I'm just echoing everyone else, but using fully half of the RAM for the OS, and thus only improving by 2.5-3 gigabytes over this generation? That sounds very out there. If it's bound to be 16GB, I hope the OS doesn't take any more RAM than it already does, what it really feels wanting for is CPU, as the PS4 OS has been janky ever since they reduced the CPU allocation to one and a bit cores.
In fact, I hope this time the ARM subsystem is powerful enough to run the system UI and most system processes, leaving the main x86 cores with just enough OS on them to run all the libraries needed by the games.
Especially with increased focus on 4K, just 8GB for the unified VRAM and game memory sounds increasingly unbelievable.
It would be awesome if they PS4'ed it, all this mislead about not being able to have that much high performance RAM, and then it comes as a pleasant surprise when they showed 8 gigs of GDDR5 at the time. If they could hit 32 the generation will be more interesting imo.