Well, bold prediction. At this point I think this unlikely, but we'll see.
After the Labo-presentation I think Switch will outsell the Wii. This is not because I think Labo will sell much Switches - I think Labo has immense support in a niche (kids and crafters). But what I see is, that Nintendo pinpointed exactly their target group before the Labo-reveal. This leads me to think Nintendo knows what they are doing, they have made their market research. And as Nintendo also claims 20M are possible for financial year 2018/2019 I tend to believe them now. This would be Wii-level, and so I see they can sell Wii-like.
Now, why I don't think (yet) they can outsell PS2 and DS (the current sales leaders). Let's take a look how these consoles reached their popularity.
First PS2. PS2 has catched a generation, with the right games, first- and third-party. It captured many target groups including casuals (Dance Dance Revolution was a thing, remember). I think the Switch can copy these points so far. The whole point of the Switch as I understand it now and the reason they named it Switch is, that the console can support a lot of different play-styles. The Joycons can be used like Wiimotes, but also as classical controllers, and also can support stuff like Labo. They even would support VR-gaming, if Nintendo goes that path. I think Nintendo knows this (also a thing I gathered from the Labo-reveal) and designed the Switch specifically for this. So like the PS2 the Switch can reach many different target audiences. BUT...
But the PS2 did more. The success of the PS2 is based on more than just that. The PS2 sold over a long time after the PS3 hit the market. This long tail added 40M. The PS2 had shipped March 2007 118M consoles and was going on until 158M shipped [1]. This was surely in part because the PS3 had a botched start, but it also means Sony supported the PS2 in the ongoing years. The WiiU was also not blessed with a great start (and in difference to PS3 never recovered). End of 2012 Wii was at 98.5M sold [2]. But Nintendo quickly killed it despite the missing success of WiiU and the console sold on to 101.6M [3]. So the Wii although exceedingly popular had in difference to PS2 no long tail, it sold measly 3-4M after the successor released. The difference is the willingness of Sony and Nintendo to support their old stuff after the new released. I see no reason this policy changed at Nintendo, so I expect they do the same with Switch. That would mean Switch has to sell more in a shorter time period than PS2. This is not impossible, but makes the thing a lot more difficult. And I have another BUT...
But the PS2 had one more advantage. Sony as an general consumer electronics company has much more incentive to dive into more and smaller markets worldwide. And they do so. Hence the success in the Rest of the World for Sony consoles. Nintendo on the other hand is a much more focussed company. They do gaming. As such the investment in smaller markets are less likely to recoup their costs. If Sony advances in a new country, they do not only sell consoles and games, they also sell TVs, smartphones, computers and so on. So financing a headquarter in a new country, placing ads, reaching out to retailers is much more likely to be a win for Sony than for Nintendo. So they are more into other countries. Look at the rest of the world sales of Sony consoles [4]. PS2 sold 25.5M. Even the more ill-fated PS3 sold 12.5M there. Look now at the popular Nintendo--consoles. The Wii has less than 10M sold in ROW. Even the DS lost against the PS2 because of ROW, only 12.5M there. And this picture solidifies (not to this extent, but still) in europe. Sony consoles constantly do better in europe than Nintendo consoles. The reasons are the same, europe consists of many countries. So, the DS beat the PS2 in markets like America and very much in Japan, but lost all this in europe and ROW. We can expect the Switch loses at least 10-15M in these markets to PS2, which it has to recoup in other regions.
Add these two BUTs together, and you see that the Switch struggles in comparison to PS2. What about the DS?
Again, the DS was woldly popular and supported many target groups, an achievement I see the Switch can do. Here I see the point mostly in that each household got multiple DS. Each kid needs their own DS. Ask yourself: can you see purchase a Switch for your wife, each of your kids and yourself? Or do you see your family use a shared or maybe two Switches? Well, that can change though, if Nintendo starts to go for this use. But it does not happen now, so we can't really expect that.
So, in conclusion: I currently see Switch matching the Wii-sales. It can do what the Wii could and more. It also got the 3rd-party-support to back this. I see at this point the Switch clearing the 100M milestone. But for 150M a lot more must be done. I doubt Nintendo can reach out into more markets, but at least they could try China and some other markets to expand their reach and make their ROW-weakness less present. Nintendo also needs to support the system after the successor is out instead of dropping it like in the past. I can't see them doing this though currently, hence I remain skeptical. Their best shot at reaching that high a number is instilling the need to get a Switch for every family member. I cannot see them doing that currently, but it could be in their plans. It is yet to see. If these things happen, they have a shot at 150M. I would currently put that at 15% chance. If we see more of the strategy of Nintendo unfold in the following years my assessment could change.
