Early this year there was a thread about the Nintendo 3ds and I pretty much got laughed at for suggesting the 3ds would still sell over 70 million lifetime.  I believe this will easily happen since Nintendo handhelds tend to sell well even after the new handheld is launched. Since this time the 3ds has been gaining momuntum and looks to be growing year over year world wide.   The only question i guess is how much the Switch will affect the system's momentum and will Nintendo at some point come out with a pocketable handheld to replace the 3ds?  Honestly I could see the 3ds selling well even after the release of the Switch since it's more of  3rd pillar to me.

3DS sales will drop next year no doubt because of the Switch BUT i can see it still selling well because of the support next year. Ever oasis, Mario Sports, Pikmin etc.

I see it do 70m maybe 73millon.

Taking this holiday into account, it is most likely above 65 millions at this point.So in my opinion 70 millions is a given, and I can see it reaching 75 millions LT.

I guess it will stop selling at the 74 million mark and crawl to the 75 million mark.

I do not think it can make it to 70 million. This holiday (which I do not think will get it to 65 million) will be its last strong season especially with Nintendo's history of pulling support extremely fast

It depends on how much Nintendo produces. They only shipped like 6 million this fiscal year.

It will probably reach 70-72 millions.

Nintendo should continue to support it, because the Switch install base will be very low for at least the next two years and Nintendo needs to sales game to the 3DS install base.

Actually handhelds they support for some time (Developers and Nintendo) after the successor device is out. For example Pokemon for the DS launched around the same time after the 3DS came out. GBA still did well after the release of DS. 

And here the 3DS will be the only game seller for quite some time.

Nintendo can't afford just to sell a few games on a launching switch.