WCCFTech reports that AMD is working on a GDDR6 memory controller for its upcoming graphics cards. Starting with an AMD Technical Engineer listing GDDR6 on his portfolio, the site claims to have verified through sources familiar with the matter that AMD is, in fact, supporting the new graphics memory standard and will be using their own controller to support it (rather than licensing one).
AMD is not abandoning HBM2 memory though. The company is sticking to its previously released roadmaps and Navi will still utilize HBM2 memory – at least on the high-end SKUs. While AMD has so far only released RX Vega 64 and RX Vega 56 graphics cards, the company may well release lower-end Vega-based cards with GDDR5 at some point although for now the Polaris architecture is handling the lower end. AMD supporting GDDR6 is a good thing and should enable cheaper mid-range cards that are not limited by supply shortages of the more expensive (albeit much higher bandwidth) High Bandwidth Memory that have seemingly plagues both NVIDIA and AMD at various points in time. GDDR6 further offers several advantages over GDDR5 with almost twice the speed (9 Gbps versus 16 Gbps) at lower power (1.5V versus 1.35V) and more density and underlying technology optimizations than even GDDR5X. While the G5X memory is capable of hitting the same 16 Gbps launch speeds of GDDR6, the newer memory technology offers up to 32Gb dies* versus 16Gb and a two channel design (which ends up being a bit more efficient and easier to produce / for GPU manufacturers to wire up). GDDR6 will represent a nice speed bump for mid-range cards (very low end may well stick with GDDR5 save for mobile parts which could benefit from the lower power GDDR6) while letting AMD have a bit better profit margins on these lower end margin SKUs and being able to produce more cards to satisfy demand. HBM2 is nice to have but it is more well suited for the compute-oriented cards for workstation and data center usage rather than gaming right now and GDDR6 can offer more price-to-performance for the consumer gaming cards.
As for the question of why AMD would want to design their own GDDR6 memory controller rather than license one, I think that comes down to AMD thinking long-term. It will be more expensive up front to design their own controller, but AMD will be able to more fully integrate it and tune it to work with their graphics cards such that it can be more power efficient. Also, having their own GDDR6 memory controller means they can use it in other areas such as their APUs and SoCs offered through their Semi Custom Business Unit (e.g. the SoCs used in gaming consoles). Being able to offer that controller to other companies in their semi-custom SoCs free of third party licensing fees is a good thing for AMD.
With GDDR6 becoming readily available early next year, there is a good chance AMD will be ready to use the new memory technology as soon as Navi but likely not until closer to the end of 2018 or early 2019 when AMD launches new lower and mid-range gaming cards (consumer-level) based on Navi and/or Vega.
*At launch it appears that GDDR6 from the big three (Micron, Samsung, and SK Hynix) will use 16Gb dies, but the standard allows for up to 32Gb dies. The G5X standard allows for up to 16Gb dies.