Too early for this memory
Volta is out for artificial intelligence, machine learning applications and it will be shipping in DGX 1 systems, mainly for deep learning and AI. The next Geforce will be a completely separate chip.
Coming in early 2018
SK Hynix has announced its GDDR6 DRAM chips, advertising them as "the world's fastest" 2x nm 8Gb GDDR6 DRAM on the market.
Updatad: The next generation
Micron has promised to launch a new kind of memory that is twice the speed of mainstreams GDDR5 . This will be released during 2016 and will be company's answer to HBM.
Exclusive: Highest end are HBM 2.0, GDDR6, GDDR5X
AMD over-hyped the new High Bandwidth Memory standard and now the second generation HBM 2.0 is coming in 2016. However it looks like most of GPUs shipped in this year will still rely on the older GDDR5.