"As an extremely niche product in Apple's lineup, the company has shown little interest in its standalone display in recent years. Inventory stockouts have happened repeatedly over the years, helping to create speculation that an update could be forthcoming, but that has yet to happen.Apple won't release a GPU-equipped Thunderbolt Retina 5K display anytime soon - report
In fact, Apple itself sells alternative displays, like the 4K IGZO Sharp LED monitor, for Mac customers looking for a high-resolution external display.
Thunderbolt technology does allow enough bandwidth for external graphics cards, which some Windows PC makers have taken advantage of, turning portable laptops into gaming powerhouses when docked. Some enthusiasts have even made unofficial workarounds for external GPUs on the Mac, but doing so requires nontrivial hacking and the result is buggy."
Friday, June 03, 2016
Apple won't release a GPU-equipped Thunderbolt Retina 5K display anytime soon - report (AppleInsider)
Looks likely we won't know for sure until >= October (as part of the next MacBook Pro intro)