Well, eventually the interest for switch from non owners will decline, even if nintendo supports it, like 3DS.
Only switch owners would buy the new games.
Also, is better to have 2 consoles selling 100 to 120M than 1 sellling 160 to 180M(that will also have more price drops).
But I see a mid ground. I see switch successor coming only in 2024 and switch having a 110 to 130M total sales.