The problem with a Retina Thunderbolt Display is bandwidth. The only mac capable of running such a monitor today would be a Mac Pro but using two Thunderbolt buses (4 of the 6 ports). The only feasible way ist to use Thunderbolt 3 wich will be released sometime in 2015. So it could be quite a while until we see a Retina Thunderbolt Display.
The problem with a Retina Thunderbolt Display is bandwidth. The only mac capable of running such a monitor today would be a Mac Pro but using two Thunderbolt buses (4 of the 6 ports). The only feasible way ist to use Thunderbolt 3 wich will be released sometime in 2015. So it could be quite a while until we see a Retina Thunderbolt Display.