3DS: 75M
PS4: 110M
Xbox One: 55M
Nintendo Switch: 100M

Currently it's still very hard to predict Switch sales, its only 6-7 months on market and its was most of time supply constrained on most on markets, I think we need at least another whole year of sales without stock problem and than to make some more accurate predictions.

Based on your prediction, do you suppose that PS4/XB1 will have another revision somewhwere around 2019-2021 instead of proper next-gen? Because if they won't that's highly unlikely that PS4 will sell that much. And your statement about Windows being the future of gaming in MS ecosystem... While I agree with it, I still don't see it coming in the near future. They've got a long way to go. I doubt Windows 10 will be able to become a decent gaming platform in the next 5 years. MS has made very little progress since last year with it. And they basically need to kill off Steam probably if they want to use Windows 10 instead of Xbox as their main focus. And the problem with MS is that they are some kinda impatient so they can give up on that idea just like they did with GFWL.

I'll go...

PS4 - 120M
Switch - 75M
3DS - 75M
XBO - 50M

I have to say it is still funny seeing people predict that the PS4 is only going to do slightly better than the PS3 and not even reach 100M.

PS4 - 140m
Xbox One - 45m
3DS - 75m
Switch - 85m

Results table updated to this post.

Also, I'd just like to say that KBG29's prediction single-handedly increased PS4's standard deviation from 10 to 15.