I don't think the PS4 will sell more than 9M this year. That's already a steep drop despite having some very heavy hitters. From there, I calculated 5M for 2021 and 3-4M for 2022+, so a maximum of 125M. And when I did that, I already took the $500-550 price tag into account.

The reason I'm not going higher is because the market will be flooded with second hand PS4 either way. When the PS3 came out, there weren't enough second hand units for everyone, so sales stayed up in industrialized countries while the developing countries just started releasing the console around those times, thus keeping it's sales up.

Hence why I compare the sales rather with the ones from the PS3 when the PS4 launched. And those went as follows:

• 8.2M in 2013 (PS4 launch year)
• 3.5M in 2014
• 2M in 2015-2017 combined

So compare that to my prediction for the PS4:

• 9M in 2020 (PS5 launch year)
• 5M in 2021
• 3-4M 2022-2025

and you'll see I actually gave the console quite a bit longer legs than the PS3 had.

And that's the reason why I believe 125M is the limit for the PS4, it's already following a very similar direction just before the launch of the next gen as it's predecessor did, and I don't see why the PS4 should do differently than the pS3 did. Because of big game releases maybe? Well, the PS3 got GTA V, Beyond: Two Souls, Gran Tourismo 6, Final Fantasy XIV and The Last of Us to name just a few heavy hitters the year the PS4 got released, so I don't see any advantage for the PS4 on that front either.

The thing with the PS2 and DS that should be understood too is those systems had massive ubiquity unique to their time period which can't really be replicated.

The PS2 could double as a DVD player in an age where disc-based movie media was booming massively worldwide, everyone had to switch over from VHS to the new DVD revolution, even grandpa/grandma. The DVD boom benefitted everyone from big Hollywood studios to even small indie filmmakers, suddenly there was a huge demand for disc product. The PS2 also had a longer "retirement" phase because it was $99.99-$129.99 and the PS3 was freaking $600, lol ... which resulted in PS2 probably selling for years longer, but this is not something Sony wanted or would want to willingly replicate. I'm sure if you gave them a choice between 150 PS2s versus 130 PS2s but PS3 going to 100+ million, they would've chose that instead, they did not think the PS3 would start they weakly.

The DS basically had a monopoly on the touch screen casual gaming market until smartphone games took off massively in 2010 with things like Angry Birds. But prior to that, Nintendo had a good long window where it basically had a monopoly on that style of gaming.

The PS4 and Switch while successful don't really have an overriding external factor going for them in that type of way, they are more or less just game machines. Which isn't a bad thing per se, it just is what it is. 

Not really the same thing. Anyway PS2 had a long protracted period of sales because the PS3 was a dog in sales for a long time because of the ridiculously high price. 

You don't want to replicate that, yeah Sony did sell PS2s, but it likely came at the expense of the PS3, causing Sony headaches for 2-3 years, which isn't a good thing. 

Console transitions are actually far more vital and key to a company's business than net total LTD. A previous system selling to some LTD is not much comfort if you transition badly to the next cycle. I'm sure when things were looking really ugly for the 3DS and Wii U, Nintendo probably would've rather had 80 million Wiis + 120 million DS' if it meant 50 million Wii Us and 100+ million 3DS' the next cycle.