If Nintendo gives up on the Switch by 2022, its being unrealistic. The Wii for selling so long lasted till this year even though by 2013, people moved on from it.
Earlier gens had an incentive to have newer consoles released for next gen due to Nintendo either wanting to do something new or that the previous gen hardware was not powerful enough to catch their visions. But the Switch is powerful enough that Nintendo can like do anything with it. So in that sense, they can make it last longer than previous gens and so, it should last a decade imo.