I don't think the Switch will have the twilight years of the Playstation 2, but it doesn't need them at this point to surpass it. Similarly, we need to remember that massively successful systems that have so much to offer new consumers don't just stop selling overnight, even if the big numbers are over. Look at the shipments of Playstation 2 vs the Switch:
At the end of year 8, the PS2 was coming off of a 13.7m year, and while I think Nintendo will miss its 13.5m projection for the equivalent year, the Switch will still be over 150m shipped by the end of March 2025, whereas the PS2 was at 131.6m aligned. But the PS2 remained incredibly steady for the next 3 years, amounting to over 21m more shipped during that time alone. So while I don't think that Switch shipments will remain that high for that long, another 10m for a system that is likely to stick around for a while as a cheaper alternative is quite doable. Even the 3DS shipped over 9m after the Switch released.
Looking pretty likely to me.
Essay Pro