Lets see if the switch can do what the wii u could not, and what the gamecube barely did-make it past 20 million units. I think the switch will sell 4-5 million in 2017, 5 million in 2018, 4 million in 2019, 3 million in 2020 and 2 million in the rest of the future. I do not think the switch will pass 20 million units sold. 

I believe ps4 + ps4 pro will sell 150 million units and xbox one + xbox one scorpio will sell 90 million units in contrast. I believe the pro and scorpio are "future proof" and will be on the market for the next 8 years.

I think so.

I think it will

Absolutelly. I have three words for you: Po Ke Mon. Well, it is only one word, but 3 is more dramatic.

I think it will be more than capable to pass 20 million, this thing has the 3DS install base behind it and a main series Pokémon game alone could sell 20 million of those things no problem.

Oh boz, tagging this for the future.Going to be fun to read these kinds of predictions.

Why stop there? Not bold or anywhere near accurate enough if you ask me. How's this?

The PS4 will sell 400M lifetime and the PS4pro is so future proof that there will not need to be a PS5. And the NS will sell -3M worldwide cause nintendo will have to pay people to own one.

Am I doing this right?

here is a reason I can think of why it should at least sell well over 20M

By the end of it's second Christmas.

The Nintendo Switch is both the new nintendo handheld and console.

The 3DS sold 61.6 million.
The Wii U sold 13.6 million.

Of the 3DS userbase, let's say only 25 million decide they want the next Nintendo handheld.
Of the Wii U userbase, let's say only 6 million decide they want the next Nintendo console.
And let's say of all of those that 10 million would have bought both the handheld and console seperately if it was the same situation as 3DS and Wii U, but now they just have to buy one single system since the Switch is both. 

That's already 41 million.

The Switch will have Pokemon, Yokai Watch, Monster Hunter, Dragon Quest, Mario, Zelda, etc, etc. All of which could get the Switch to and PAST 20 million just by themselves.

So yes, I imagine the Switch will easily surpass 20 million. 

It will likely easily pass 40million. The PS4 will not be anywhere close to 150million, and the same goes for X1 reaching 90million. I think the X1 will have a hard time passing 50million to be honest.