Well ... given that the camera is at a distant most of the time ...does it really matter
that much?
Also I wonder with DX11 coming, how much VRAM they really have to spare. DX11 effects might end up using even more memory (more and higher quality render targets).
Increase texture resolution also means you have to add more mipmaps to prevent texture aliasing - that obviously cost memory too. (To be blunt, FFXIV could use a few more mipmaps, or maybe it's just the LoD bias set wrong, as texture aliasing is quite severe as it is.)
FFXIV to my knowledge uses about 600-900MiB of VRAM at the moment. I have a 2GiB card. How much of an improvement will we see if they double the number of pixels in the textures ... it's hard to tell - might even be barely noticeable.