GDDR6 the successor to GDDR5X and HBM3 are scheduled to be released in 2018.
GDDR6 is cheaper than HBM3.
HBM3 allows for 64GB's and allows for more than 8 dies to be stacked together.
http://www.neogaf.com/forum/showthread.php?t=1268040
This is probably why Microsoft and sort of SONY aren't going to be sticking to consoles for five years or eight years anymore and instead will be releasing new consoles every what three years?
I can't wait for GPU's that have 64GB's of VRAM and like 40TFLOPS of GPU compute power.