3DS games require more work than DS games and Switch game require more work than Wii games.

Based on your logic, they should "be able to do so because the Switch is 7th gen in complexity", as opposed to the 8th gen complexity of the PS4 and XBO.

No, 7th gen tier is labour intensive enough, we saw that when they tried to support 3DS and Wii U at the same time.

It was for the Wii U because Nintendo wasn't yet used to producing games in HD (their own admission). They needed to create new tools to accomodate that. Those tools, and experience, are now there from the start for the Switch. 

Exactly why they basically have no choice but to support Switch with everything ... price drops, all their games, all their marketing, etc. 

They can't go back to the dual system set up, it's too resource intensive among several other problems with it. 

For better or worse Switch is it. Any "alterations" are simply going to be made to that existing product line (ie: price cuts, smaller models, bigger models, you name it, etc.). 

Come on dude, I know you're smart enough to know that making Mario Kart DS + Mario Kart Wii is obviously less work than making Mario Kart 7 + Mario Kart 8, for the same reason 2D indie game takes less manpower than a AAA blockbuster.

Yes, but it's not as bad as you make it seem. Tools improve over time. Engines become for efficient and easier to work with. Things balance themselves out. Even if it takes more people to make some kinds of games, there are tools that weren't in place before that now allow people to make technically sound games for a lot less and with less manpower than before. Firewatch is one of many examples of that. 

Everything is negative and blown out of proportion bad with you. Isn't it tiring over time?

Extremely. And I'm sorry, I do try not to do this, I should probably just stay away from VGChartz these days so as not to be a drag, but as I'm bored, on holidays, and have nothing better to do, I keep drifting back, and the negativity of my offline life spills into my online life. Again, I apologise.

I edited my comment.

If it can hit 40 million by the end of 2020 ... I mean it's not exactly "lets throw a party" type numbers, but it would be a good deal enough to ensure a Switch successor, you're probably looking at a LTD finish of 50-57 million in that case.

*If* Nintendo can get a new IP that really, really breaks out (or Splatoon 2 explodes like wild fire) then I would revise up from there, but I think this is for now a reasonable estimate. 

It's still tough out there compared to what the DS/Game Boy/GBA had to compete against .... 3DS and especially Switch have it much harder, even the 3DS was somewhat insulated as smartphone adoption wasn't quite so high (especailly with kids) and tablets were still relatively an expensive item the early years of this decade. 

And certainly there weren't like massive multi-million dollar ad campaigns for smartphone games, that would've been unheard of in 2011 as 3DS was launching, today a lot of the most popular games in the industry are mobile games and they have marketing that dwarfs even Playstation/XBox games. 

So a lot has changed.