All 4k & 5k displays made next year will need displayport1.3. How many macs support this? NONE.
That's same for all current Graphics cards as well.
The Dell 5K display needs two Display 1.2 ports just to drive it as well.
Both AMD, and NVIDIA are only talking about supporting above 4K now.
http://www.tweaktown.com/news/40597...-toward-8k-resolution-or-7680x4320/index.html
So it'll still be a while, and then monitor manufacturers and their controllers still need to catch up as well.