https://www.sie.com/en/corporate/release/2011/110214.html

PR statement from 2011, at the end it mentions that Eastern Europe, Middle East, Southeast Asia & South America are the primary markets where it is still selling well.

PS2 legs were mainly due to these regions, PS4 did not have this issue of a super slow start and explosive later growth in these regions so PS4 legs coming anywhere close to PS2 is not happening.

One thing I haven't seen mentioned is how well Nintendo's other handhelds have performed. Here is a brief rundown of each of Nintendo's handhelds by global sales

Keep in mind too that the GBA was cut off early so it was only on the market for about 4-5 years. But as you can see, the average for Nintendo's handhelds is 107 million. This is already about where the PS4 is at. Switch only needs to sell a bit more above the average which is very doable. Nintendo's Q3 results aren't out yet but so far Switch sales are up about 30 percent through the first 6 months. 

I think this assumption that it can't happen is really driven by people looking at the console side and not the handheld side. There is a reason Nintendo made a hybrid system.

GBA was cut short but on the other hand Gameboy had an insane sales curve thanks to Pokemon & GBC causing it to peak in its 10th year and went 12 years before getting a successor which is unheard of so I think they cancel each other out.

Emerging markets were the main reason why PS2 managed to sell a ton of hardware even after the release of PS3, but now PS4 is readily available in those markets since 2014. In the southeast Asian countries, you can easily get the megapack deal of PS4 with 3 free games(GOW+GTAV+HZD) and 3 months of PS+ subscription at $250 while Nintendo Switch + Zelda BOTW bundled is around $400.

25M yes, but how much of these 25 have been sold after 2006 ? 10 to 15M at most. Even if we remove these 10-15M of the PS2 sales we still get a little over 140M, so PS4 has real chance of reaching 140M with of course the proper price cut, in the right time and good support of 3rd party games after PS5 launch.

I was wondering why we say "switch 2 " like it may be a completely different console in terms of sales... and why we won't calculate switch + switch 2 vs ps4 + ps4 pro... Cause all these sales of PS4 are ps4 + ps4 pro (Gen 8 + 8,5 or 9 or I don't know :p )

For the same reason we won't add PS5 sales to PS4 sales. And technically speaking, ps4+ps4 pro is competing against switch+switch lite+whatever future revision that will not have its own exclusive games.

Eastern Europe isn't surprising when these are the dates of attaining EU membership:

2004: Estonia, Latvia, Lithunia, Poland, Slovakia, Slovenia, Czech Republic, Hungary
2007: Bulgaria, Romania

Every country that has joined the trading block has experienced accelerated growth in wealth due to free trade across borders and it takes at least a couple of years until it really manifests in the spending power of the average citizen, hence the late blooming of the PS2 in Eastern Europe. Like you say, the PS4 could take advantage of that right from the start.

Other regions have also experienced general economic growth since the PS2 days, hence why the PS4 has been officially available in more than 120 countries within one year of its launch.

Yes, that's what I said in my conclusion: in my opinion, the switch will outsell the PS4 probably after 2023. I was just explaining why i think it will. 

Yes, it was just an observation.