A few months ago I would have expected it to fall just short of 130 mil, but since lockdowns around the world has given all consoles a bit of an unforseen boost, I think it has a good shot at 130 mil now. Anything more than that I doubt though.

I think the PS4 will sell for quite some time after the launch of the PS5 because of Cross-Gen titles. It could very well become the cheap option to play most games, Sony could drop the price to 199 or even 99. In such a case I expect the PS4 to overtake the PS2 in the long run.

I could be horribly wrong of course. =P

125-130m. If it gets notably more than that, then it probably means the PS5 launch went wrong.

125-127m seems about right with 10m max for this FY then a creep up to the mid/late 120's by the end of it's lifetime.

My biggest question has to do with price cuts.  What is going to be the final price when PS4 discontinues?  If you had asked me 2 years ago, then I would have been confident that Sony would have cut the price by now.  But there hasn't been a price cut since it hit $300 in 2016.  PS3 final price was $269, which IMO was too high for a final price, but that is what they did.

I think 125m if there is no price cut, and 145m if they go down to $200 at some point.  I'm going to try to read their mind and say the final price will get to $250-$270 price range.  So I voted 132.5m-135m.

Bonus Answer:  I've never needed to use Sony's online service even when it was free.  I don't pay for it, but I do pay for Nintendo's.  If there are enough people who think Sony's service is good enough to pay for then it should be a paid service.  Basically let the free market decide if it is a valuable service or not.  I don't see gamers as a political group any more than any other group of consumers.

In the case of the XB1, Microsoft was trying to take gaming in a direction that gamers didn't want it to go and that is why those "features" had to change.  I remember the Microsoft execs saying, "You can't stop the future from happening", but in this case gamers did actually stop that particular future.

125M-130M.

As for the bonus question, you could ask Nintendo fans the same thing about their online and Nintendo's reluctance to lower game prices so that poorer gamers can enjoy them, too. I guess everyone makes excuses for their preferred brand. Though, at least Sony gave away games, didn't lock apps/F2P games behind the paywall, and offered deep discounts. Before, MS's model was to take as much money from gamers without giving much in return.

Somewhere in the 125-130m range, since it'll continue selling after PS5 launches, much like the PS3 with the PS4 release.

I think it will cross 120M by the end of this FY and 125-130 end of life
BONUS: Yes gamers should have taken a stand since Gold was created and certainly again when Sony put the multiplayer behind PS+ and also when Nintendo followed with an even poorer option.

125M if Sony planned a relatively quick transition to next gen, 130M, even 135M, if Sony planned a slower one, with PS4 staying longer on the market as entry level console. Anything more is less likely, it would require not only a big price cut, but also a few new cross gen games and a decent schedule of older games budget versions, and probably a super slim restyling too, and all this done in time, as if the sales curve flattens at a level too low, lifting it again to viable numbers would require, if even possible, an excessive investment compared to possible profits.

So, to cut it short:
125M with little effort and no big mistakes
130M with some more efforts and no mistakes
135M with some more efforts and everything going the best way
More than 135M quite unlikely, requiring far more efforts, perfect timing and a lot of luck. Most probably not worth the investment, that money could be better spent to make a cheaper PS5 version possible earlier.

I don't think that's true.

You can still use a lot of internet based services that are subscriptions elsewhere. without PS+ you can still use party chat, share screenshots, live stream to twitch and other services. Use all of the streaming apps like netflix, etc. (Although I think that last one MS changed their minds so you can use it without any XB live if someone can correct me on that?)

And you can still play online on F2P games as well without PS+.