Plausible. The console market is cyclical, after all, though the peaks and troughs are getting less pronounced, especially if you take Nintendo out of the equation.
The PS4 and XBO are already down YoY, enough to where the Switch is so far not making up for it to keep the U.S. console market as a whole from being down. They are almost certainly going to decline even more next year as the launch of the PS5 and Scarlett eat into their sales, and the Switch could very well decline, too. We may not see combined PS+Xbox console sales start to rebound until 2022, and the console market as a whole might not grow again until the Switch's successor is released, which may not be until 2023.
As for the market for dedicated handhelds, that's pretty much over and done with once the 3DS is discontinued, that is unless Nintendo is planning a handheld-only version of the Switch.