10 million is an extremely conservative projection by Nintendo so, yes, hardware units wise they probably will be at #1 this year. That said- revenue wise they'd probably need to sell close to as many Switch's as PS4's to match as the 3DS (and particularly the new 2DS XL at $150) sell for considerably less.
will be interesting to see who ends up at #1 this year mainly because the Switch looks strong and then NIntendo has a much larger boost from the 3DS than Sony with the Vita