Reaching waaaay back for this one, but I think it's fair to take another look at this now. We have hit the end of the generation more or less, although it does make things a bit awkward that the Switch doesn't line up with the other console lifespans.
Correct any mistakes I make, but it looks like we have the following numbers.
PS4 - Sitting at about 115M, with the likelihood of coasting a few million more over the next year or two. It should end somewhere short of 120M.
XB1 - Concrete numbers are harder to come by, but it looks like this will probably end just above 50M.
3DS - Sliding in to home with 76M. Good for you, old friend.
NSW - Sitting at 80M as of the end of 2020. Where will it stop? Nobody knows. I think 2021 will give us a much better idea of that.
Looking through the thread, there are some pretty good estimates in there! Also some not so good guesses.
I think there are too many variables to make any kind of reasonable estimate, so I am going to eliminate some. I don't know how long current generation sales will last, what type of hardware iterations are coming, or whether they should be counted with current gen sales, so I will cut my predictions off at Dec 31, 2020.
LTD sales, Dec 31, 2020
PS4: 111M
XB1: 65M
NSW: 90M
PS4 sales have been very strong, and should continue to be. However, I think that this year is the peak and that we will begin to see a substatial decline from this point on. An early announcement of new hardware could drive sales lower, while a major breakout in emerging markets could drive sales higher.
70M by end of 2017
17M 2018
14M 2019
10M 2020
XB1 has been relatively weak, but there could be some increased strength going forward. I think the 1X will have a bigger impact than many suspect. It is a very attractive, well made piece of hardware. It provides a much more substatial upgrade to purchasers than the PS4 Pro did. I think it will appeal to core gamers, which in turn will give some exposure to the ecosystem and stave of its apparent sales collapse. This will not be enough to make the XBox a contender to win the generation.
35M by end of 2017
12M 2018
10M 2019
8M 2020
NSW looks poised to be a monster success. Obviously its first holiday season hasn't come yet, and we will have a much better idea where things will stand after Nintendo gives us earnings for this year and an outline of next year's lineup. I've seen a lot of improbably low, 50-60M lifetime (even 40M!) predictions for Switch, so I am going to stake out the optimistic ground a bit. The obvious pitfalls for Nintendo, which could cause sales to be much lower, are failing to keep up a steady launch cycle, failing to meet production demands, or failing to meet fan expectations with Pokemon for Switch.
15M by end of 2017
20M 2018
30M 2019 (Yes, best console year ever.)
25M 2020
So, how do I think I did? Let's break it down.
I think the end of 2020 was a good place to measure from. I give myself 1 merit point for realizing that in 2017.
PS4 - My total numbers weren't too far off, but the yearly breakdown was a lot worse. Sony held very strong sales late into PS4's life with a lineup of incredible exclusives, which left overall sales higher than expected. However, the PS4 was also taken out back and shot a lot faster than previous Sony platforms. 2020 was weird. I don't know if PS4 sales would have been higher or lower without the global pandemic.
For PS4, I rate myself 'pretty good.'
XB1 - I was way off here. I really thought that the One X was going to revitalize the platform and that it would see its strongest years at the end of its life, like 360 did. That just didn't happen. Microsoft stayed pretty consistent through the generation and ended with the same middling sales they started with.
For XB1, my mark is Unsatisfactory.
3DS - Things were pretty clear when OP was written. 3DS was already at the end of its life, and it limped along for a couple years after. I didn't make a 3DS prediction.
For 3DS, I receive an A+. The only way to win is not to play.
NSW - Ooooh, boy. I'm the only one in this thread who can be definitively said to have overestimated Switch sales. I was trying to stake out the optimistic ground, though, so I will give myself a bit of a pass on that. My numbers assumed that we would get a very compelling Pokemon game at the end of 2018 which would drive strong sales. I also assumed that we would continue to see a strong and constant software slate like we did in 2017. Both of those were wrong, and sales reflect that fact.
For NSW, I will take an E for Effort.
Overall, I rate my guess as 2.22... out of 3 stars.