Only a small number of high-end cards like AMD's Greenland and NVIDIA's Pascal will feature HBM2 memory. GDDR5 is still being improved and we can expect cards with more capacity in 2016, as well as the first models with GDDR6 memory, which promises higher bandwidth than GDDR5 but lower cost than HBM2.
Some of the big boys, including Samsung and Micron, have started producing 8 Gb GDDR5 chips that will enable cards with 1GB memory per chip. The GTX 980 TI has 12 chips with 4 Gb support (512MB per chip) while Radeon Fury X comes with four HBM 1.0 chips supporting 1GB per chip at much higher bandwidth. Geforce Titan X has 24 chips with 512MB each, making the total amount of memory to 12GB.
The next generation cards will get 12GB memory with 12 GDDR5 memory chips or 24GB with 24 chips. Most of the mainstream and performance cards will come with much less memory.