I would say that an RTX2080Ti die that is massive on 12nm TSMC would be comfortably manageable on 7nm Samsung or TSMC. Anything bigger might take a bit longer to arrive, more maturity required. Most indicators are Nvidia won't launch 7nm parts until early 2020. The process should have had an entire year of mass production by the time Nvidia need stuff ~500mm² churned out.
Nvidia could gain 25-30 percent performance across the board with their current RTX lineup for the same power envelope without even bothering to tweak the design specifically for 7nm. Radeon 7 is evidence of that.
One assumes Nvidia will also go for more architecture advances, realistically we could see an uplift of 40 percent on Nvidia's GPU range. 7nm will be very welcome.
After Nvidia's 2020 7nm GPUs we could be in for a seriously long generation, surpassing even Pascal's lifespan. Moore's law is long dead. I plan to buy the fastest 7nm card I can next year, and I bet it won't be significantly surpassed for at least 3 years after that.....