Hmm, so less than 160K gap once October numbers are known. I think Xbox One X is going to eat into PS4 more than Switch, guess Black Friday is the big question. Switch won't get a discount, and PS4 will get a $100 one. But Switch will be THE hottest Christmas Gift this year. December is a dead month (Xenoblade looks good but it's not pushing consoles imo), and November only saw third party Switch released, albeit big ones. Also Mario momentum. I think that if Switch has stock it can win, and it should have a good amount. But if Sony buries November in Black Friday sales, then December may not be enough to climb back.
I'll give Switch 80% chance to be the best selling system of 2017.