Considering the previous consoles 130 or 140 millions is more likely than 120 million.
It seems impossible to reach PS2 numbers, because who the hell can beat 155 million consoles. But if, and only if, PS4 reached $99 in the next 2 years, I think it would be doable. Of course, it might be a pipedream since Ps4 BOM cost must be way more than $99.
It took 5 years and 9 months for PS2 to reach 100 million units sold and PS4 will beat this record. PS4 only reduced it's price a 25%, which is less than PS2 did and starting from a more expensive price. Next 2 years PS4 will be packed by great exclusives/marketing rights and we'll start to see the Spiderman and RDR2 effects now. It's very likely that PS5 won't be released until a couple of years from now, and that will be full BC. If there is BC and indies can put their games on PS5 by releasing them on PS4, PS4 will continue getting many games so it will have a post PS5 library very similar to the one that Switch got this year.
Sony always supported consoles (and they sold) after their successor release. They can marked PS4 or PS4 Pro as a low end, sub $200 PS5 due to BC and if they want by including PS5 games in PSNow. I think it's more likely to see 130 or 140 million but I think 150 may be possible