Here's my two cents on it. PS4 has plenty to push sales this Christmas, possibly including another Black Friday deal. The real concern for its sales is that the console is finally approaching market saturation, whereas the Switch has a much larger base of customers that may want one but don't own it. A lot of its heavy-hitters this season are also available on PC and Xbox, which will fragment things somewhat (though those games are still most likely to sell best on PS4).
This year, the PS4 is down a bit over last year. Next year, the PS4 will likely be down over this year. It'll still sell great but slowly decline until the PS5 is announced. Switch is (so far) on an upward tick because it's newer and just as popular as the PS4 was in the same time-frame.
The only thing that can stop PS4 is its age. The dragon is getting old.
God bless You.
When PS4 will hit 100m consoles sold: Before Christmas 2019
There were three ravens sat on a tree / They were as blacke as they might be / The one of them said to his mate, Where shall we our breakfast take?