AMD will get an efficiency bump from the shift to N7 and hopefully some tweaks to GCN. Last roadmap I saw showed Navi being geared towards a performance increase and ‘ Next-Gen' being geared for 'efficiency' (significant architectural changes).Possible if NAVI has no RT cores/hardware and AMD makes some serious efficiency improvements over Vega.
I’m assuming most of the performance improvement for Navi will come from a frequency bump and ,hopefully, at least a small increase in the number of CUs. I wish RTG had the resources to put out two Navi dies this year so they could better compete with NV - but I’ve seen no credible rumor to this effect. Maybe RTG will be able to introduce a scaled up Nave design in 2020 to fo along with the next-gen Instinct design due that year.