According to Mat Piscatella "Next Gen consoles sales will not have a major effect on Switch sales"

[VAMatt]

Depends on the definition of "major". I could see the next gen systems cutting a couple million units off Switch. The next gen systems will get more media coverage, and they'll be more often requested on Xmas lists, etc. But, I don't know that we'll even be able to tell, as Switch sales will be more affected by other factors than by the launch of PS and XB.