It looks like GPUs have changed their advancements from "tick and tock" advancements, to tick-tock ones.
Nvidia:
Kepler - Die Shrink and new architecture at the same time.
Maxwell - New architecture on the same node as Kepler.
Pascal consumer GPUs - the same architecture as Maxwell, on new node.
Pascal GP100 - new architecture on new node.
Volta - (appears to be) reused GP100 architecture on the same node as Pascal consumer GPUs.
AMD: Tahiti - brand new architecture, made on new node.
Tonga - new architecture, on the same node
Fiji - same architecture as Tonga, with tweaks on the same node.
Polaris - variation of the Tonga/Fiji architecture made on new process.
Vega - new architecture on the same process as Polaris.
Vega 7 nm - same architecture, ported to 7 nm process.
Navi - next generation architecture on 7 nm process.
So It appears that we are at max 2 nodes from the end of silicon. And 7 nm will not be here till 2019-2020.