So, in the future, we might be using 2560×1600 (HiDPI) mode on a theoretical 30″ 5120×3200 pixel display. All user interface elements would stay the same size as today’s 30″ Cinema Display, but when available, higher resolution textures would be used to render the graphics. This is the same way that it worked when Apple transitioned from the original iPhone resolution to the iPhone 4’s retina display.
Except for the next iPad, which is rumored to sport a 2048×1536 Retina Display, I’ve got a feeling we’ll need to wait a bit for pixel-doubled displays for Macs. I hope I’m wrong.