There is a reason why the memory will not sufficiently be used to be worth adding, that being that the supporting hardware does not have the bandwidth to use the ram effectively, the APU does not have the raw power required to drive the data bandwidth needed to make adding additional memory worthwhile, and when your target framebuffer is 1920x1080 or less, theres only so much texture data that can be displayed before adding more resolution to the texture data becomes a waste of bandwidth - sure its nice to have pretty textures that are still pretty when your face is right up against a wall, but no developer is going to waste the system resources to add additional texture detail that for 99% of the time you will not see, for two very good reasons.

1) adding that level of texture quality is extremely costly on the creators side

2) the data thats put into memory needs to first be put in to memory to begin with - assuming they took 4gb of ram of system, and left 8gb for video - even if we assume they used only 2gb of ram for textures, to support these textures you would also need to bump up the lightmaps, bumpmaps and shader quality - resulting much of your memory available being used - AHA! i head you scream, SO IT DOES USE IT ALL!, yes, indeed it would, but then you would need to wait for that data to be loaded from hard disk to memory, or from optical disk to mem, both of which would take a long time - and for the former, it would also mean that games take up a substantially greater amount of hard disk space and given that the xbox one has a fixed, non-swappable hard disk that would be a stupid choice.

But i digress, if any of you would like to point to *ANY* game, mods installed or otherwise on PC that uses more than 4gb of vram at 1080p then I will hold up my hands and say "okay, i might be wrong", but until then, youre just ignoring the reality of the situation.

System memory is used primarilly to load meshes, sound and textures that are not time critical, which are then passed along to the graphics unit to be processed, or placed in vram to be accessed faster when needed, this is an entirely abritrary process however, you can run a modern game on a pc with a decent graphics card with just 2GB of system ram, typically the system ram is used to stream game data from hdd to system ram to speed up load times and provide faster data pool switching but this is primarilly a result of the inefficiencies of a modular system, a closed system like a games console relies much less on this process than you are suggesting, because data can be loaded from fixed media directly into whichever memory pool the program defines - but the end result is the same, even if you split 8gb down the middle, a decent spec PC even with its inefficiences as a platform, with 4gb of video ram and 4gb of system ram, will still run games at 1080p perfectly fine and even then will still NOT FILL UP ALL 4GB OF VRAM.

Even if current engines magically "evolved" as you put it, there is a platau with regards to renderspace and framebuffer bandwidth, a large part of why there is still such a push for faster more powerful graphics cards isnt because engines demand it, its because modern monitors resolutions are getting higher, and with them the power and resources needed to feed that video data requirement grow - people who are still using a 1080p monitor and an old graphics card are still able to play modern games just fine.

But i will say it again

the PS4 and Xbox One, do not have the CPU or GPU power to use more than 6gb of vram effectively at 1080p, if you started pushing more texture data through the framebuffer you would just be deminishing the performance, 12gb of ram would not make the system better, 12gb of ram would impact the framerates in exchange for an extremely minor bump in graphical fidelity.

I was waiting for this. Thanks. Some people have no idea of how the manufacturing process works. Seem to think you can just change specs "overnight" and it's that easy. Systems are already on the production line.

When epic games told microsoft to double the xbox 360 ram it cost microsoft $0.5 billion.