If we assume PS5/Nextbox release holiday 2020 we're 18 months away.. I could see PS4 take a couple if LoU pt2, Death Stranding hit stores in this period (they should) but outside of that.. I'm not sure how many months Switch would lose in that span.
At this point, I don't think any single game can give the PS4 a win unless it's in a really slow month like what May is shaping up to be. It feels like Sony has gotten just about every major audience they can and all that's left are the bargain hunters waiting for a huge price drop or sale.