PS4 is still 180k up this year in Japan thanks to Monster Hunter, so I don't think there is any need to panic after a quiet month. We know it's not going to sell great at any point in Japan anymore but it's still going along well enough.
16m seems like a good estimate. Not sure why people think this makes a Q1 2019 release more likely. Who would replace their console when it's still selling 16m a year and nearing 100m sold, and making you well over a billion in profit? Sales so far this year show the PS4 is selling great without a price cut, so why rush it? Go along nicely for the rest of the year, have BF sales, and cut the price Feb/Mar 2019. Then you have Last of Us 2, Death Stranding and Ghosts of Tsushima to push sales also.PS5 is going to be 2020 for sure.
16m is a quite incredible forecast for a consoles sixth financial year. And 264.9m software in one year is phenomenal too