If I had to make a guess, the estimate is based off the end of december NPD numbers, since Janruary NPD isnt out yet for the companies/research firms/investors/etc, which will be February 15. The public release at February 22.
So yeah, like others have said its probably a bit over-tracked here.
35 Million lifetime for the end of 2017 sounds about right.
Bet with Intrinsic:
The Switch will outsell 3DS (based on VGchartz numbers), according to me, while Intrinsic thinks the opposite will hold true. One month avatar control for the loser's avatar.