I'm curious as to why OP keeps insisting that current Thunderbolt ports can't support a QFHD (3840 x 2160) display. Thunderbolt layers a few lanes of PCIe with

I'm curious as to why OP keeps insisting that current Thunderbolt ports can't support a QFHD (3840 x 2160) display. Thunderbolt layers a few lanes of PCIe with a DisplayPort 1.2 signal. DisplayPort 1.2 supports QFHD at 30 bits/pixel and 60Hz. Of course you'd be limited to one display per port, and I'm not sure whether that much bandwidth on the DisplayPort lanes would crowd out the PCIe traffic. Alternatively (as anyone who bought Macs in the 90's can attest), Apple has never been particularly reluctant to introduce a new interconnect when it was convenient for them. Obviously if they simply pixel-doubled their current 27" panel it would be far beyond Thunderbolt's capabilities, which may be where the "Thunderbolt can't support Retina resolutions" idea originated.