I can understand there are doubts for a 3 million December, not this year, but in general.
Doubts for a 2 million December? Can't understand why and how. It is obvius that for Nintendo, the trend of November being almost the same as big as December isn't there yet, unlike Sony and Microsoft.
But even if it was, we saw November/December this generation being >1.5 million for PS4, one time even for XB1. There is no reason to believe is impossible to ever see a 2 million December for a console in a particular situation in a particular year.
PS4 for example already has the potential, is just limited by Sony, and i'm not gonna talk about the reasons or whatever, i'm saying that IF SONY WANT, it could easy sell 2 million PS4 in a December.
And we are likely gonna see Nintendo do that as well this year and next year.