It won't because the bandwidth of TB2 cannot transfer the amount of data needed for a 5K display. The new Retina iMacs can get away with it because it can interface with the graphics output directly.

Hmmmm my math can be wrong but I don't think you are correct:

5120x2880 = 14745600 pixels

14745600pixels x 3 colours, 1 byte each = 44236800 bytes

44236800/1024/1024 = 42.19MB each frame

42.19MB per frame x 60 frames a second = 2531.25MB.

TB2 has a bandwidth of 20Gbps = 2560MB/s

So yeah, theoretically TB2 has enough bandwidth. But it's a very tight fit.

Displayport (and HDMI) have a 2 bit ECC overhead for every 8 bits transmitted, so effective bandwidth of DP 1.2 is 17.28 Gbit/s. Additionally, the timing adds additional overhead, so the required bandwidth is actually 22.18 Gbit/s for 24bpp 60Hz 5120x2880

The above calculation was for 32bpp:

3 colors * 1 byte * (8 bits/byte) = 32 bits

I am sorry,but no it wasn't. 3*8 is 24 not 32. But in any case I don't think the display requires 32 bits, alpha is not necessary.

Thanks for the clarification. fwiw, I knew that alpha wasn't necessary, but vaguely remembered that DisplayPort might support displays that expected the entire 32 bit word to be sent. Looking at the specs, I don't see that. But it does show that DisplayPort supports 16 bits per component, or 48bpp.

FYI, Wikipedia's section on DisplayPort lists the resolution of 5120x2880 x 24bpp @ 60Hz as requiring 22.18 Gb/sec of bandwidth, see http://en.wikipedia.org/wiki/DisplayPort#Specifications

Even if the GPU does, DisplayPort 1.2 doesn't support 5K displays.