In an official Question & Answer summary published by Nintendo Shigeru Miyamoto said that he could imagen that the Nintendo Switch would break out of the normal life time cycle of current video game devices. The normal life cycle is around 5 - 6 years, while he would like to see that Nintendo can manages to let the Switch be longer on the market. (read the Q&A here)
In my opinion this really could happen. Even if the Switch is not a real replacement for the Nintendo 3DS, I somehow see it like on the same level. And as the 3DS got released in February 2011 it reaches now the 7 year, still getting support from Nintendo and third party producers.