While the Polaris GPU architecture is to be released this year, two new architecture (or product series) code-names have surfaced in a roadmap shown in an AMD presentation, Vega and Navi.

It seems that after Polaris in 2017 VEGA will make an appearance, the name is tagged with HBM2 meaning that HBM2 likely will not make it onto Polaris. Vega is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus. Next in line in the 2018 timeframe we see Navi with the two keywords being scalability and Nextgen memory.
  

 
The slide is plotted in years/time against perf per watt, so you will notice that the perf/watt ratio almost makes a 2x step every new release. It will be interesting to see how ling AMD stays at 15nm, 7nm is obviously the next step in fabbing, that technology is due for release in 2019/2020.