It'll be interesting to see what Apple does then because 2X the current Thunderbolt Display (how Apple has done hiDPI)would put it above 5k.

Maybe it will take a future version of Thunderbolt using optical cables to do a Retina Thunderbolt Display. Or maybe Apple will simply make it around 4k.

Apple do the 2x stuff on iOS so that the large set of handcrafted, bitmapped 1x apps can map precisely to pixels when you upscale them. OSX doesn't have the same issue, since there's no existing default screen size that is designed for.

Apple is doing 2x on OS X as well. That's how the new Retina MacBook Pro works.

This allows Apple to give users the same exact workspace as before, just with 4x the pixels.

They could break this with the iMac and Thunderbolt Displays, but 2x is how I expect all Mac laptops to be in a few years.

Makes one wonder whether we'll see 21" retina iMacs / Cinema Displays before the 27" versions.

Since Thunderbolt is also some sort of PCIe port, couldn't you have the GPU be internal to the Cinema Display, and transmit only the GPU code over Thunderbolt? Or are significant parts of the screen drawn by the CPU directly these days?

I suppose that would be possible, if the built in GPU has local video RAM and such. You wouldn't nearly be consuming the bandwidth compared to sending raw video to the display.

I do think it would be a little too complicated though, it's probably more likely there will be a faster Thunderbolt port before that happens ;-)

Latency is a much larger problem.

Is there higher latency between Thunderbolt connected components than "regular" PCIe?

Yes. Even with PCIe "extender" ribbon cables of a few inches, you can stumble over latency issues.

Falcon Ridge will deliver 20Gbits/sec per channel (40 total), making the 5K iMac possible. But we will have to wait until 2014.

Doesn't that assume no compression in the transfer? Surely, if streaming compression is getting better, there's some lossless compression that can be used for display signals?

What does your video card/monitor do when it's asked to display a frame that can't be compressed?

Generally these things would have to be done in hardware, bumping up the price by a non-negligible amount. Additionally, it would increase the input lag on the monitor, something manufacturers are trying to avoid.

It would have to be real-time (60 frames a second) and I just don't see significant savings being possible anytime soon.

The new Macbook Pro Retina has two Thunderbolt ports. In theory, they could build a display using both, each driving half of the screen. Although it's unlikely to happen.

Similar things have been done with large displays in the past, though not on consumer hardware.

Would that not be pretty similar to dual-link DVI? Though I believe that was part of the DVI specification whereas I've never heard the current Thunderbolt standards to have provision for such. Regardless, I wouldn't be shocked for Apple to do it at least initially in their own non-standard way.

Dual-link DVI is still one connector. Needing two separate ports to drive a monitor is pretty un-Apple.

hm but i have seen Thunderbolt Macbooks running two 27" Cinema Displays: http://www.youtube.com/watch?v=sP1thwUcO9c

A retina Cinema Display would have the pixels of four Cinema Displays.