The amazing thing about the Switch is that Nintendo should have enough games already developed or in development for it that they could have at least one big game (including ports) releasing every month for all of 2017.
For example, in any random order these games could release any month outside of confirmed dates:
March: Zelda (confirmed for launch)
April: Mario Kart 8 Deluxe (confirmed for April)
May: Arms
June: Splatoon 2
July: Pikmin 4
August: Smash Bros. Switch Port
September: Super Mario RPG X Rabbids game
October: Xenoblade Chronicles 2 (apparently coming out in 2017)
November: Pokemon Stars
December: Super Mario Odyssey
Also all the 3rd party games releasing or 3rd party exclusives we don't know about yet.
So the Switch should have an amazing first year with a new zelda, a new 3D mario, pokemon, and more all in it's first year. All those games each month should keep the sales consistently good.
So I think the Switch will sell very well for 2017.