Even if adding more resolution makes you unable to resolve the pixels, you can still always see light, in the same way you have no hope to resolve stars, but you can clearly see their light.
Luckily once we get oled, it no longer matters, because there is no backlight and you can always set misbehaving pixels to black.
My 24" display, at 1920x1200 (~86 PPI) is 2,304,000 pixels, and even with a moderately high end graphics card, it struggles under load. You're talking about a display with 18x as many pixels to paint (or, to put it in a metric more easily graspable, it'd be like running ~18 displays at 1920x1200 @ 86 DPI, across which a single frame would be painted.
Needless to say, I don't think that technology is going to be showing up in stores near us in the next year or two. :)
