As I mentioned in the other thread, there's just not enough bandwidth to drive at 60fps over a single bus / single cable with DisplayPort 1.2 without compression (DP v1.2 gives about 17.3Gbps usable bandwidth which is just not enough). The iMac allows them to bypass that bottleneck by interfacing directly with the graphics card.

My predication is that once we see Apple deploy Thunderbolt 3 / DisplayPort 1.3 (capable of 25.9Gbps usable bandwidth [1]), we'll see the Apple Cinema Display Retina.

[1] http://www.extremetech.com/electronics/190130-displayport-1-...