NVIDIA first revealed the Volta codename in March 2013, at the time the goal was to achieve 1TB/s of memory bandwidth on Volta.
We expect to see Volta using HBM 2 memory for the GV100 part and the GV104 - the GPU version of the chip is likely to use the GDDR5X with some Titan versions possible with HBM 2, but only if being really pushed by Vega.FUD Zilla expects the first Volta GPUs will hit the market before the end of Summer, but these will probably be parts for the data center market. Some parts will adopt HBM2 but the more affordable consumer versions will probably launch with GDDR5X.