Looks like the PS4 is going to be super close to the 80M mark by E3 as was discussed previously in some thread.
I say there are at least 80% chances of the PS4 passing the 100M mark by the end of its cycle and If I must venture a guess I'd go with 110M lifetime.
Assuming a November 2020 PS5 release, the PS4 should have sold well over 100 million by the time it launches. I expect 90-95 million sold through by the beginning of 2019. Then it will sell another 15 million at least in 2019, then there's 10 months of 2020 before PS5 releases. Keep in mind the PS3 sold 8 million in 2013, expecting 10-12 million for PS4 in 2020 isn't too crazy.
We could be looking at 120 million PS4's sold by the time the PS5 releases (being optimistic), but at least 105 million (being conservative). Then don't be suprised if it sells another 15-20 million after that before it's off the market. 130 million is my lifetime estimate, but I'm not disregarding the possibility of it selling more than that.