This is an extreme statement. You think Switch could outsell PS4 by 900k in just December? Smash will be huge, but that would almost certainly require a 1.9m+ month, which is PS2/Wii/GBA/DS levels. Switch is not selling anything like those machines right now. And I don't think PS4's December will be as low as last year, which makes the target even higher.
I think Switch definitely has a chance to outsell PS4 this year, but not by so much in a single month. I'd project PS4 to do 2.7m in the holidays (marginally less than the last two years). So if Switch has a ceiling at, say, 3.5m total (only Wii has ever been notably higher), then they need to be less than 800k behind by November. Right now they're 300k behind. I believe they'll drop back by another 100k in September, but reasonably flat in October. So beating PS4 will not require a legendary holiday, just a very good one. But if they somehow exit November 500k back, it'll be a challenge.
No they didn't. Switch sold 400k units less than PS4 or XB1 in the holidays. My personal prediction is that Switch will outsell PS4 this holiday, by a lot. But a $199 PS4 with ample supply would alter that.
If Sony do 3m this holiday--which is what +250k versus last year would be--then Switch will have a hard time catching them for the year. Not impossible, but it'd require a historically-huge performance. And after launch month, Switch has just never been putting up those kinds of numbers.