It is always funny to see what people always note down on their linked in pages. This time it is a principal member of AMD's technical team, Daehyun Jun. His entry states he is/ was working on a DRAM controller for GDDR6 memory. 

Currently, the linked-in page has been edited, and now just mentions "DRAM controller". It's all simply, HBM in any form and format is still expensive and difficult to use. If anything, the vega launch has shown exactly that. So it makes all the sense in the world for AMD to pursue a cheaper technology, and with GDDR6 being very promising, they started designing a new controller for their GPUs.

 
GDDR6 has the potential for double the bandwidth over current gen 8Gbps memory as used on say a GeForce GTX 1070 Ti. It's good news as we know it's coming likely on the next wave of graphics cards, also it uses less voltage and can theoretically double the bandwidth over current gen GDDR5 memory. To compare a little, current GDDR5 memory on say a Radeon RX 480 /  GeForce GTX 1070 is roughly 7 or 8 Gbps, and GDDR5X on a GTX 1080 can do 10 or 11 Gbps.
 

 
GDDR6, when released, will start right where GDDR5X will end, at roughly 14 to maximum 16 Gbps. his means more bandwidth (up-to double over current bandwidth) and higher clock frequency memory. Voltages wise GDDR6 will be rated at 1.35v, which is exactly the same as GDDR5x. Other companies like SK Hynix and Micron are on track with GDDR6 as well.

GDDR6 will probably be available from early 2018.

AMD Working on GDDR6 DRAM Controller