Depends when the PS5 comes out, but maybe in a couple or so years

1) thats not true.

Its selling better 2017 so far, than it did in 2016.  These are facts.

That means its not passed its peak year, but that 2017 is looking to be the best year for it so far.

2) Nintendo switch has been on the market for months now..... and it hasnt slowed the sales of the Playstation 4.

Again these are facts. Sales of the PS4 are up YOY month by month, even with the Switch out to compete with the PS4.

Your reasoning doesnt make sense, if you actually look at sales.

Sales say what you "think" so far is wrong.

After 2019's holiday, so i say January 2020

Just give it up JRPGFAN there is no reasoning with these guys. They insist that the PS4 won't sell over 100 million units. I think it will take a bit longer than expected but still it's just pure bias to think otherwise. Anyway if that's the route people choose let them. Although it does fascinate me that people think that a console that sells so much better than the PS ONE isn't going to surpass it. The only reason Wii didn't sell more was because Nintendo cut it legs and Sony isn't going to do that.

They're going to sell 100mm units this week, once they announce that they're dropping the price to $99 at E3.

It wont if they plan a PS5 in a couple of years.
But like most Sony consoles, they will keep selling the machines for 10 years and claim how good there consoles sell.
PS4 will outsell Wii if PS5 doesn't come until 2021. However that's a long time to let MS sell Scorpio as the most powerful console.

2019

The 10 million isn't 2020, it's April 2019 till March 2020, by the end of that Fiscal year PS5 would have been out for 4 months.

Excuse my poor choice of words. By "kind of stagnated" I meant that so far in this calendar year, we don't see those crazy total YoY growths as we used to. Mind you, we just passed month four (data wise), so it might mean nothing, but the trend is quite obvious, as seen below.

Holidays this year lol