How much do you think Switch would sell in The US? Last year US sales made up 37% of Switch sales and if the switch sells 18m US sales would be around 6.6m but the Switch is tracking behind the PS4 in the US and the PS4 is tracking behind the PS4 in 2017 so i think its reasonable to thing Switch could sell 14m.
With regards to the PS4, what its tarcking right now doesn't really mean much. Especially when you consider that last year the PS4 was weakest during the holiday season but reachs that 20M figure because of how well it did throughout the year.
In 2018, its not doing that well compared to 2017 but its no slouch either and we are yet to see whatever boost GOW is goingto have on sales. But If sony decided to drop the price around the holidays for a longer duration of time then it could at the very least match last year sales.