This.

Yes, it should have just about shipped more than the NES by the end of March 2017, when 3DS should be at 62 million. I expect life-time shipments to be in the 67-70 million range.

Assuming the NX is effectively a successor/replacement to the 3ds I expect the 3ds to reach around 64-66 million.

I think it's almost a certainty it will break the 62 million mark.

I would be surprised if it didn't

Crazy things happen. Like theres games out there that we think it will do bad, but it turned it around. And vice versa. 

I'm surprised many people expect under 65 million lifetime for 3DS.
3DS is at 59.79 million by end of June 2016, before the Pokémon GO phenomenal, after July NPD and the many European region boost we saw (UK, Italy for hardware, as well Germany and France for software), i see 3DS selling AT LEAST as much as last year from now (but will most likely be even up).

3DS sold 4.77 million last year, i think it will probabily be at least 5 million this year, i personally say even 5.5-6.5 million, and of course, it won't stop selling just after NX, Nintendo will most likely continue to sells 3DS even in 2018-2019.

70 million seem the most likely scenario.

I have no doubts about it.

True, but a comparison is a comparison nonetheless. VGChartz still posts vs. articles that pit Wii U vs. PS4 and Xbone and we all know how that's going, or PS4 vs. Vita. It's just for comparison's sake.

to be fair, the ds and gameboy were dirt cheap. I myself owned about 6 game boys and 3 ds'. Cheapest I've found was 40 bucks for a refurbished ds during 2007.