We've written a lot back and forth about GDDR5X versus HBM2 (and GDDR6 these days). Nvidia did not place all their eggs in one basket, AMD pretty much did so for high-end. That being the main and root cause of delays as HBM2 is difficult to fab and expensive. As it stands now, opcoming consumer GeForce cards based on Volta will not use HBM2.

This is a new claim that originates from Fudzilla, who states that this info came from well-informed sources. I tend to agree as nothing is pointing or indicating towards HBM2 from Nvidia at this moment in time. From the looks of it, small and compact HBM2 memory simply is too expensive for consumer products. Nvidia does use HBM2 on its GV100-gpu, but much like what happened with Pascal, here again they will revert to GDDR5X memory for the consumer parts.
 

 
While HBM2 might seem to offer better memory-bus width, latency and lower voltages, it seems harder to fab and implement and likely thus is more costly and complicated to use than expected. Just look at the massive AMD Radeon RX Vega (consumer) delay, this likely is due to the limited availability of HBM2. Meanwhile Nvidia has been plastering GDDR5X in their recent high-end SKUs. GDDR5X still rocks hard this year. Next to HBM2, GDDR6 is the new thing for 2018. The new graphics memory type will offer up to 16Gb (2GB) per IC. So eight ICs would already get you to 16 GB of graphics memory.

Nvidia could make use of SK Hynix and/or Micron GDDR5X memory. 

Upcoming Geforce GTX Volta cards Use GDDR5X not HBM2