That seems pretty far-fetched.

How will it sell another 50 million from here on out when it's likely less than 6 months away from being replaced?

Considering some reasons I seem people throw for Sony sales numbers the answer would be "they will just keep selling the console until it reaches 160M in 30 years"

The same way the ps2 did, many replacement consoles for broken consoles, and a proper price drop to reach many poorer countries, I know a lot of people back in Portugal and Brasil that are still waiting for a huge price drop both on ps4 and second hand games, people who can't afford to pay more than 150 euros

The ps5 will cost 500 euros, maybe more, 1 game will cost 70 euros, thats 570 euros, the ps4 with one game for 150 euros seems like a better deal for poor people who don't even have a 4K TV.

And then there's a lot of PC and Xbox people who might get one just for Last of us 2, thats going to be the biggest game launch of the year by far, no point in paying more than triple the money just to play one game.

PS4 isn't breaking and needing replacement at anywhere near the rate the PS2 did, PS4 already released in the emerging markets that PS2 didn't get around to until much later, and Sony holding $300 this long suggests they do not plan aggressive price cuts.

And one game this late in a console's lifecycle won't alter its entire trajectory.

 You need to travel more, back in Portugal I barely know anyone with a ps4, many people are buying ps3 right now for the very cheap games and free online. 

Sony can and will drop the price, I guarantee you that, I don't know what you are on but 300? I've seen ps4 slim for less than 200 already several times.

You must be naive to think ps4 doesn't break, I had one just a few months old that was having graphical glitches, many people complain their disc drive doesn't work, or hdmi failures, everything breaks, as long as its electronics.

You don't think one game can affect sales? Do you want to bet? Let's wait and see sales of the ps4 when last of us 2 drops. The ps4 is guaranteed to sell 7 million until christmas. Many parents can't afford 570dollars gifts for their kids.

One more thing, I have been following gaming for 30 years, I know Sony, I am not sure the ps5 will release this year in Europe, USA yeah for sure, Europe, maybe February/March, also there won't be enough stock anyway, Sony will not have enough SSD to make more consoles, a lot of people will be looking to find one until next year.

Your firsthand experiences aren't a big enough piece of the global picture to be relevant. 

And PS4s are far more reliable than PS2s, the latter were notorious for the disc drive dying.

Sony have said the want to move people from PS4 to PS5 faster than previous generational transitions, so clearly pushing for the highest lifetime PS4 sales is not their plan.

What sony wants and what really happens are 2 very different things. These new tech SSDs will not materialize out of thin air.

Sony also can't sell the ps5 for less than 500 dollars, and even at that price they will be losing money per console sold, so business wise they'd rather sell less at the beginning.

Sony also can't force parents to spend minimum 570 dollars if they could spend 200 for christmas gifts. The customers always set the market, not sony or any other company.

Hit the wrong one, wanted to click the one above. My guess is 124M but I clicked 125-127.4M

And that market is already near saturation point for the PS4. The people with a $200 Christmas budget will have gotten one for that much at any one of the last three holiday seasons. After six and a half years, there just aren't that many people left who want one that don't already have one.

I don't know what planet you live in, but ps4 is selling about 1 million per month right now, before Last of us 2, before ghosts of tsushima, I really don't understand your logic.