Here's something interesting, an investigation of recently released AMD graphics drivers for the Linux platform revealed references to what appear to be Navi-based GPUs.
AMD's current Vega GPUs were codenamed GFX9 and these new drivers feature a line that refers to GFX10 "SUPER SECRET":
new_chip.gfx10.mmSUPER_SECRET.enable [0: 0]
VideoCardz speculates AMD uses SUPER SECRET instead of the actual codename to avoid generating hype. Navi is expected to be made on a 7nm process and earlier slides from AMD indicate it will use next-gen memory, which could be something like HBM3 or GDDR6.
The site says Navi is currently slated for a late 2018 launch, so don't get your hopes up for a speedy release.