Sadly, I think retina iMacs are further away than we'd like to hope. Eizo has a 36 inch 4K monitor for $35,000¹. There's a 31 inch 4K Viewsonic Monitor for an undisclosed price². Even that's only 150dpi. If Apple wants to make a pixel doubled 27 inch iMac for under 10K, I'd be surprised it if they could do it by 2013.

But then again, I thought the retina MacBook Pro was impossible. So perhaps I'm not the best judge of these things.

1. http://www.geeky-gadgets.com/eizo-showcasing-its-35000-4k-lc... 2. http://www.engadget.com/photos/viewsonic-vp3280-led-31-5-inc...