And how big exactly is the portable market for CoD, FIFA and GTA? 

-GTA did 5m and 7m on PSP and that was the portable gimped versions. What option is there for anybody who wants to take GTA with them? Smash Bros is doing fine on portable, Street Fighter did fine considering you needed 2 systems for local multiplayer. RE Fifa and CoD, we've never had a system with portable local multiplayer but we know that it is/can be a massive boom to a title's success.

"Nintendo handhelds can do ~70M minimum" As the 7th and 8th should have taught us by now, the gaming market doesn't follow out silly "rules" such as this one.

-Ignore the DS and Pokemon is doing fine, Mario Kart is doing triple the sales of the GBA and 2D Mario has doubled. It seems to me that not having the Brain Training and Nintendog crowd on board has been more detrimental to 3DS. Whether that's because of smartphones or dumping simple stylus/touchscreen games and threatening to blind your kids with 3D, who knows?

As far as combining libraries; the same first party franchises were available on 3DS and Wii U that you could get on Wii and DS, and yet the former pair managed a fraction of the software sales and will end up below or around 1/3 of the combined hardware installed base. So combining two into one won't automatically improve sales beyond this, there's no logic in that, especially seeing the price tag which makes the Switch a very expensive handheld, alternately a home console priced similar to the competition but with much less power and developer support. Yet another poor argument in the big picture. Not to mention dual-ownership, which is quite common.

-Combining libraries will improve hardware sales, software sales could suffer. Instead of 2 Karts/Smash/2D Mario/3D Mario/Animal Crossing/Mario Maker, Nintendo can make one of each and have 6 new IPs too. That also ignores the fact that for example, Pokemon is now on the same system as Zelda. Having Pokemon makes the system more attractive to Zelda fans and vice versa.

Motion controlled fitness games making a comeback? Why on earth would that happen? 

-The market didn't kill Wii Sports/Fit, Nintendo did. The idea that 8yr olds from 2006 loved Wii Sports but the 8yr olds in 2017 won't enjoy it is silly. Same goes for dance games, Quiz TV party games, music games. Nobody's buying a PS4/PC for those.

Would the 3DS have sold better? No idea, it would certainly have cost a lot more, and it barely moved at its original launch price, so there is that. It's all hypothetic hindsight though, and is, unsurprisingly, yet again a useless argument in this context (but a fairly interesting idea). Having the bigger franchises on a handheld doesn't mean all that much either, the Vita had a lot of these big titles and it still sold like something close to the opposite of its hilarious name.

-I think portable local multiplayer is being underrated. There is the possibility that Candy Crush multiplayer or Fruit Ninja party mode is the best thing ever (not saying it is, just saying adding multiplayer to ANY game can make a huge difference). Nintendo is offering local multiplayer, buttons, gimmickry to smartphone games and local multi, portability, gimmickry to PC games.

Look; I'm not saying that I have to be right, but it strikes me that most of the arguments for a huge, Wii-like success for the Switch is based on flimsy grounds and made up "rules", a lot of suppositions and wishes and desires rather than a cold, hard look at market realities. There is no logical grounds for thinking 100 million hardware sales by what we've seen or know, there just isn't. And mega hits don't just "come out of nowhere", they are a result of riding trends, striking broad and solvent audiences and offering a somewhat lasting appeal. There's a huge chasm between "I want this to happen" and "This is likely to happen due to market circumstances and current and impending movements", as of today, March 21st 2017, there is very little basis for the latter but there's a whole lot of the former going on. A lof of people in here seem hell bent on "revenge" for the poor Wii U sales and the massive decline between the DS and 3DS, and that's probably a lot of the reasoning behind these immense predictions, there are very few other explanations for it.

-If I take 3DS 70m as a minimum, remove the 3D and add a better gimmick, add a new Wii Sports/Fit, take into account how well PSP did with console quality level games (GTA,GT,MoH,NfS), look at the potential from indies/smartphones/PC, increasing 1st party output, getting an extra 30m on top isn't so hard, imo.

- The X-factor: Nintendo has a habit of massive new IPs but even if one comes from a 3rd party it still works in Nintendo's favour. If a new IP CoD/GTA-level comes along then Nintendo might miss out on the full version but could still get a gimped portable version. If it's a breakout like Minecraft then portability and local multiplayer could make it the definitive version.