These are the 3DS latest figures per Nintendo

https://www.nintendo.co.jp/ir/en/finance/hard_soft/

Hardware:66.12miilion units ( As of March 31, 2017 )

PSP final figures are harder to find but Wikipedia has the following 

Worldwide: 82 million, rounded-up (as of November 2013)^[1][2][3]

Vgchartz has the PSP final figures at 80.82 million for reference. 

Nintendo foreceast that they will sell 6 million additional 3DS by march 2018. If they manage to do so the 3DS sales will stand at rougly 72m. From there on they will need to sell 8 million (or so) more  units to pass the PSP. 

Personally I think it will be very close and will heavily depends on how long they keep supporting the 3DS after 2017 but they will manage at the end (just barely). 

Thoughts? 

So 16m 3ds's sold post-switch... probably not.

It could, if the Switch wasn't around.

With the 3DS still having games like Pokémon, Metroid and Dragon Quest coming out for it as well as a whole new hardware revision, it's certainly possible. If they can get the 2DS XL price down to $99 by 2018 and still have great titles come out for it, I think it's almost certain to at least hit 80 million lifetime.

No. Nintendo still needs to sell 16 million more 3DS-es and I simply don't see that happening. It wont be far off, but if they are expecting 6 million this year with the last big hurrah, I doubt it will sell more than that in the remaining years especially if they figure out how to produce more Switches. IMO the 3DS had 75 million locked and maybe they can stretch it to 78 million, but not more.

It ll fall short by a bit I feel.

The 3DS needs 3 more good years (including the current one). I can see it happen this year, and maybe it will not drop too much next year, but no way it gets a good third year after Switch gets a main Pokemon.

So it will fall short, probably around 75M after all is said and done.

If they support it well and have good price cuts they have a shot. I still think it'll round out at 78-79 million and fall just short though.

You know the GBA is another interesting comparison

It had a final figures of 81.51 million according to Nintendo .

Didn't realize it sold so close to the PSP.

Nah it'll fall short. Could still top 75m, but not much more. It's too bad, the system deserved more sales, and to outsell GBA.