You have a good point, I'm sure games on a 30" retina-type display would be absolutely gorgeous. Perhaps the rumored 3GB of VRAM on the 7970 and 7950 will come in handy. By the way, is there a point to using anti aliasing if the pixels are too small to distinguish?
Some form of AA will always be necessary. Games are generally overlaying one thing on top of another, with no blending, and if the items have high contrast, it just looks wrong. Especially when everything is in motion. It's hard to explain, still images don't even tell the full story, but your brain can tell it's just not right.
My opinion is that some form of AA will be necessary, but that the pixel density increase will minimize the advantage that the hardware intensive forms of AA hold now (at low pixel density). With 4x or 9x the number of pixels, Cards will also not have the performance to spare for these intensive forms of AA.
But it is possible that at some point we eliminate the need for AA altogether. The performance impact of FXAA is so small though, that I'm not sure there is a huge need for it.
As for VRAM sizes, 4x the pixels would have similar memory footprint as 4xMSAA does now and 9x pixel density would have similar footprint as 8xMSAA. So there wouldn't even be a huge memory impact over what we're using now... except if you were adding 4xMSAA on top of that resolution.