I can see the Switch having a five to six year life span, going beyond that probably would be only possible similar to as the 3DS is still being supported right now when outside of a few games it is pretty much dead. While I do think both Sony and MS are not going to rush out their new systems any time within the next 3 years, expecting the Switch to go beyond 5-6 is madness unless they plan on doing a "NEW" model with stronger architecture which now that I think about it is probably very much in the cards.