Micron and SK Hynix have been in volume production of GDDR6 for several months. Samsung is also in volume production of GDDR6 which will afford the video card manufacturers with adequate supplies into 2020.
This will afford AMD with an option to revamp Polaris with the faster GDDR6 memory for sale into the mainstream market. nVidia has adopted GDDR6 for the recent RTX 2000 and GTX 1600 lineup of cards. AMD has the RX 5700 and RX 5700 XT with 8 GB of GDDR6 available. Many more video cards will be released as GDDR6 replaces GDDR6 across the industry.
GDDR6 is less costly than HBM which is important for keeping costs under control. Considering that video cards are now transitioning from 8GB to 16GB the cost of memory becomes important.
The move to GDDR6 with the Samsung 10nm line will improve the performance to some extent. They are making 16 gigabit chips so it’s easy now to equip a video card with 16GB without resorting to placing memory in the solder side. There is some need for 32GB video cards for professional use which are now possible with the Samsung memory.
The need for more unified shaders has become important as the move to 4K panels becomes prevalent. nVidia presently has more extreme cards than AMD but competition will change that over time.