While Vega is barely out of the doors, AMD is already moving forward to NAVI. Graphics cards based on these 7nm fabbed GPUs would be released in August 2018 according to new information. 

Website TweakTown stated to have information about Navi, but does not mention a source:

Once again I have an exclusive story that AMD will have Navi ready to go sometime in July-August 2018, with a Navi-based professional card being launched at SIGGRAPH 2018. We're still waiting for AMD to launch Radeon Pro SSG, something they unveiled during SIGGRAPH 2017 that hasn't yet materialized.

I must state that personally I find next Summer a bit early for this part, as 12nm refresh for Vega is far more plausible. Little is actually known about Navi, other then we know it's fabbed at 7nm of course. AMD’s Navi GPUs will be built using GlobalFoundries’ 7nm node using 7LP technology.
 

 
“Thanks to additional improvements at both the transistor and process levels, the 7LP technology is exceeding initial performance targets and expected to deliver greater than 40 percent more processing power and twice the area scaling than the previous 14nm FinFET technology,” was stated by GlobalFoundries back in mid-June.

AMD Navi based Graphics cards Might Arrive in August 2018