aside from all the other comments people have made, you also seem to think that nintendo just couldn't have decided to go a new direction? these comments made by miyamoto (who, mind you, does not have as much power in decision making as he used to) were at the nexus of the switch. things change, businesses change, and, in nintendo's case, leadership even changes.
i'm sure miyamoto hoped that they could elongate the switch's lifespan to 8-10 years. but, business needs trump hopes and, in the end, like
@Terrell said, they kind of already did succeed in expanding the generational lifespan. 7 years is one step closer to 10 than 5 or 6.