I don't think one is even possible until Intel releases Thunderbolt 3.
Transferring True-color 5120x2880 at 60 fps requires at least 25GBit/s connection, and no existing connections (on shipped computers) can handle that. The best ones currently are Thunderbolt 2 with 20 GBps, and DisplayPort 1.2 with 17GBps.
Only just a few weeks ago, DisplayPort 1.3 was released, which tops 32Gbps, and upcoming Thunderbolt 3 is promising 40 Gbps. Those two are finally making honest-60fps 27" Retina Display possible, so it should not be long until we see one. (Though of course that will require Apple to update all Macs with Thunderbolt 3 or DP 1.3 ports first)