I'm going for 70m by 2020 and then onward to infinity and beyond.

more than xbone

At least 7 billion.

Is it supply constrained?

More than the Wii U, that’s for sure.

Well supply isn't meeting demand yet.  Amazon price is now down to 120 (used) and 133 (new) though but that is still 40-50 over retail price.  If supply met demand then you could pick one up off Amazon for 80 dollars.

https://www.amazon.com/Super-NES-Classic-nintendo/dp/B0721GGGS9/ref=sr_1_3?s=videogames&ie=UTF8&qid=1511968034&sr=1-3&keywords=snes+classic

The NES classic is the definition of "Supply Constrained". - At least you have a chance picking up the SNES classic.
Got both myself. (And the Mega Drive and Atari Flashbacks.)

Something like 2 million was for the NES Classic if I recall, supply is definitely orders of magnitude greater than that was for the SNES.

70m? It's a device that appeals to a specific niche, fans of retro gaming and Nintendo. It is not a device with mainstream appeal, it could never sell 70m by 2020.

There isn't 70m people on the planet that want to play Snes games.

I voted for 10mm, because the proper choice - 100 Trillion - was not included.

How many people in the world today?

That number.