I personally feel like it will fly than it will die quick like the Wii.

Nintendo will need to hit every note for it to get that high.

well i have bought about 15-20  3DS consoles lol. So who knows what Switch ma bring for me.

it wont even reach 100m, let alone 150m. it will have the handheld market to themselves that could mean 3ds and vita numbers combined so around 90m

The TL:DR version:

1) its gen 9 cuz I say so.
2) Nintendo handhelds are always successfull, it ll still sell well even after 7years

conclusion:
its both a handheld and a homeconsole, so it ll sell like both combinded.
= 160m+ sales.

Thats basically what The_Liquid_Laser wrote in OP.

Its bold, and hes not the first to think the Switch could sell like a combination of both a homeconsole + handheld.
I personally dont think the switch will sell that much, but I guess time will tell.

Common... its mainly the "its both" so it ll sell like "both combinded" and thats hardly a new way of thinking.
Or required alot of "though out planning" before writeing OP.

I still think the overlap sales, and higher price point, could be too big a hurdle for that to ever happend.

it could sell more than the Wii did, but I dont see it going much higher.

won't even beat PS4 sales, let alone PS4 + 3DS

as people have mentioned, there is a lot of crossover between handheld and home console Nintendo owners for obvious reasons that won't buy at least two units now they are combined. I also don't see your last point, about Nintendo Switch being the biggest home console because it will have a huge library of games, as making any real sense - it will probably have 50% the amount of games the PS4 ends up with at best. Price is also a factor, with Switch launching at $100 less than its current competition, it encourages more people to jump in earlier, but means it will likely have worse legs. And that is what I am expecting - Switch to match or slightly exceed PS4 sales in the first year or two, but then slip behind and stay there. I do not think Switch will sell over 20m, for instance, in it's fourth year like PS4 just managed

I don't think so, 80 million is my estimate.

I will revisit this thread in a couple of years :p

I think Nintendo will replace it in 2021 in way of a Switch 2/Switch 4k, and the sales will fall off a cliff at that point. So unless the Switch starts selling 30 million per year, it isn't going to happen. 

Both the PS2 and DS's circumstances were quite unusual.

PS2:
-Came out during the DVD player craze as an inexpensive DVD player
-Pretty much had 1 year (or more in some regions) on the market by itself as a next-gen system with heavy marketing (DreamCast was on death's door and GC and Xbox were still not released yet)
-Continued to sell well and receive software support even after its successor was released
-Little in the way of competition from smart streaming devices and smart devices

DS:
-Picked up kids and core gamers (which is what Switch is attempting to do) as well as older casual audiences
-Had a much cheaper price point
-Little in the way of competition from smart streaming devices and smart devices

I don't think that any dedicated video game hardware, barring very unusual circumstances, will reach those numbers. The only one that I can possibly see (and I cannot emphasis how slim I think the chances of this happening) is the PS4 if it manages to reverse the home console versus portable trends in Japan (maybe MonHun will do that, which will damage the Switch in the long-term, or maybe it won't) and somehow stays on the market and continues to sell well going into its 10 years (this would almost require for them to botch the PS5 as badly as the PS3 in its initial life and MS to basically provide little competition on the stationary side).

As for Switch, I see many uncertainties in the future. For one thing, I wonder how much of an impact MonHun World will have in Japan (a market that is critical to a handheld's success). In a very bad case I can see this game stifling Switch's momentum and potentially even damaging the prospects of handheld systems in the Japanese market (certainly in the short-term I fully expect that PS4 will outsell Switch in the next few weeks to few months due to the MonHun effect combined with Switch's stock problems and lack of a similarly powerful games series in the immediate future; they key will be if this game can reverse the handheld gaming trend and make PS4 the dominant system in Japan at the expense of the Switch's momentum, which would be very bold, but still, based on the hype and the strong push of this game by Sony and Capcom that I have been seeing, quite possible). Switch is also going to need more evergreen software releases from Nintendo; there is still a lot of such software left (2D Mario, Mario Maker, 2D Zelda, Animal Crossing, Smash, Pokemon, etc) but release timing it going to be key. If Nintendo releases these titles too far a part with little software that captures the interest of gamers then they can lose momentum. Another issue is the lack of the older demographics that purchased systems like the PS2 and DS (and even Wii and the original GameBoy); these people have likely moved onto smart devices and will be difficult to court back. Moreover, in the kids market there is far more competition now from smart devices (parents may opt to give their kids a cheap tablet or their older smart devices as opposed to spending $300 on a gaming system; at most the Switch at its current price will be picked up by family units as opposed to individual children in the family). The 3DS came out when mobile gaming was still young and it had to significantly reduce its price to get into the kids market; ultimately I believe the Switch will also need to do the same.

I think the Switch in its current state will get into the hands of core gamers and be picked up families (Nintendo will need to maintain a good and desirable software output to maintain momentum with these groups). At its current price I do not see parents picking up multiple consoles for each child in the household. Moreover, I do not think it has the appeal that Wii, DS, PS2, and even GameBoy had with older casual adults. Now Nintendo can remedy some of these things by introducing smaller revisions to replace the 3DS with at a lower price point or even by dropping the price of the current; this in conjunction with titles like Pokemon might get the system into the hands of multiple children in a single household. They can also release some casual games aimed at older adults (mental fitness, physical fitness, and games like the Wii Sports series), though with the penetration of smart devices getting this particular audience back is going to be more difficult. Ultimately, if Nintendo sells this Switch model generally at this price for the remainder of its (say 6-8 year) life then I think we will get numbers that close to but below 3DS (provided they do not dramatically lose momentum with core gamers and families, which I think we will get a clue of based on software releases/sales and system sales in 2018; moreover, the system needs to be able to overcome the current MonHun craze in Japan and there is a risk of this damaging the system's momentum in its second year). Now if Nintendo dramatically cuts the price of the Switch and/or makes a less expensive model, maintains a consistent software output, manages to regain its momentum after the MonHun launch in Japan then I can see it reach or even slightly exceed 3DS sales. If they do everything I mentioned in the last sentence and also release more casual software for the older demographic as well then I can see it coming in close to but below the Wii's life time sales. Of course, how long Nintendo keeps the device on the market will also be key. The situation in Japan right now with Monster Hunter and PS4 I would say is the biggest threat to Switch at the moment, and overcoming that will be key to maintaining the system's momentum as Japan sales are going to be key.

I have argued, how I can't see it reaching PS2 and DS, but I realized a main point of your is adding together PS4 and 3DS sales. I feel like I should address this.

So, it sits not too well with me, just lumping together sales of two consoles. It assumes there is one homogenic blob of home console players and one equally homogenic blob of handheld players. The overlap was already adressed in other posts, but I don't even think the overlap is the most important point here.

Every slightly successful product does not only address one target audience, it adresses multiple audiences. This is true for successful consoles. It is a reason BTW, why I can't see PS4 reaching PS2 numbers, as they at least miss out on the casual crowd with Dance Dance Revolution back in the day, and cannot recoup that on other areas. The same is true for Switch.

See, if you add the numbers together, you just assume every home console user and every handheld user is drawn in, just because Switch can be used as a home console or as a handheld. But each of the two groups has differing audiences. And as I said before Switch is designed to address multiple audiences, but it still does not address everyone.

Let's start with some audiences of the PS4. This includes guys going for high end graphic and power. The Switch never can match that. It can't match the power of the PS4, even less of the PS5. Even if we compare with WiiU, the Switch don't make a step up in power you would expect for a pure home console. As some don't care about mobility, this does matter for these target groups. But given, the power junkies are a small group. But bigger is the group choosing he best platform for the multiplatform game they like (instead of going for the version of the game on the platform they own for other reasons). Switch cannot outdo FIFA, COD or AC on PS4, even less on PS5. Look at the differing specs of Dark Souls Remastered. Sure, the Switch-version has mobile, but as I said that is a different target audience. The audience looking for the best graphical advanced version of the game will not get Switch.

There are more target groups purchasing the PS4. Each not big, but they add up. This includes the achievement-fanatics and the online voice chat crowd, something the Switch isn't supporting (so far?). And we have networking effects. In case of consoles: you purchase a console your friends have. Especially if you want to play together with them.

But a biggie are the Playstation enthusiastics. People underestimate brand power. You included the Nintendo fanatics with 3DS, but also the Playstation fanatics with PS4. This will not work that way. Nintendo can work on increasing their brand power, but they just cna't capture the crowd following another brand. So this is also missing.

On the 3Ds-side of things you lose also some audiences. I can see for myself: I have my 3DS with me on a daily base. The Switch only on bigger and longer travels. It is bigger, more clunky. While the 3DS fits in many pockets, the Switch does not. The clamshell-design is a big pro for the 3DS here. So this reduced mobility will be important for some in the 3DS crowd, so they'll skip Switch.

Also not to forget price. Handhelds usually are pretty affordable, which helps in purchasing multiple devices for one household. The Switch price is more prohibitive. And yes, price-cuts are possible, but so they were for 3DS, which mean it has lowered it's price over time and probably will do so at least one other time. If your price starts higher, it'll end up higher probably too. This'll exclude some more.