PS4 tier mobile chips will be available by next year actually. The tech is moving very fast. Nvidia has already finished the Parker, which would be the successor to the Switch's Tegra X1 ... they are now well into development of Tegra Xavier, which will debut in 2019 or so. The Xavier chip will give you PS4/XB1 tier graphics.
The model ranges may be different Switch 1/2/3 may not be it, you might have Switch Pro, Switch Alpha, whatever.
I know such chips will be available and very likely so do Nintendo but I doubt they'll release NSW2 in 2 years instead I see them using that tech in 5-6 years giving NSW a good run while the successor will be vastly affordable by then as well falling more in line with their company approach. This is why I don't see SKUs with differing chipsets as well, it's not only easier for them to manage but also for their consumers.