When you see Intel's plans to push desktop resolutions to up to 4K, the bandwidth needed to run those resolutions is going to be monstrous.
1920x1200 = 2.3 Mpixels
2560x1440 = 3.6 Mpixels (1.6x times bigger)
3840x2160 = 8.2 Mpixels (3.6x times bigger)
4096x2304 = 9.4 Mpixels (4x times bigger)
4800x2700 = 12.9 Mpixels (5.6x times bigger)
Bandwidth needed to move all those pixels in the future is going to be something like 1 TB/s minimum imho.
GDDR5 with a 512bit bus is a good beginning. With 5-6 GHz GDDR5 you have 320-384GB/s today.
8GHz GDDR? with a 1024bit bus equals to 1 TB/s.
Time will tell.