They can keep making 3DS but it just doesn't have much of a future. Yearly shipments are hovering in the 7 million range these days, by 2019 it'll be completely dead.

If they wait until 2019 to throw their full support behind Switch, it may be too late to save it.

No one knew any of that before hand though. No one. Everyone thought it was a joke and laughed it out of every forum it was brought up in. The Switch hasn't released yet. When it does, and fails, then you have a point. Let's wait and see.

That's very unlikely, there's never been more than 2 gens for the same console:

Game Boy: 1st and 2nd Gen (RBY/GS)

Game Boy Advance: 3rd Gen (RS)

Nintendo DS: 4th and 5th Gen (DP/BW)

Nintendo 3DS: 6th and 7th Gen (XY/SM)

The only time this could have happen was with DS and its massive success but now there's no way 8th Gen will launch on 3DS again.

I think the point I'd put ou there is that the OP should just wait and see as well because none of this is evidence for shit, just circumstantial.  It's very similar to how JohnLucas would never accept the idea that the PS4, which at the time of its release was the strongest console that gen, could somehow win the sales of that generation because it hadn't happened before.  The pattern of "the strongest console has never won a gen" was just random and had more to do with price then actual console power, it wasn't an iron clad rule.  In the same way, these corollaries between wii and Switch or WiiU and Switch are all circumstantial and we should simply wait to see what happens.  

To you original post, people also thought that the Ouya was going to sell like shit, and it did.  People thinking something will fail is not an indicator that it's like the Wii.  

3DS is still getting Fire Emblem Echoes and Warriors; I can see Nintendo being too chicken to release mainline exclusive Pokemon on Switch and wanting to stick to 3DS's larger userbase at the expense of Switch's future. Ditto for Capcom with Monster Hunter; they've resisted upgrading the series above 6th gen graphics for 13 years.

Use the grandma test: show it to your grandparents and see if they have any interest.

If no, do not expect Wii-like results.

They passed away in 2003 and 2007, respectively.

Nintendo is domed. Doooomed!

I never said thinking it's going to fail=success. I just wanted to point out that a Nintendo console had, at one time, been the subject of every joke and ended up winning the entire generation so as to make him take pause before jumping to conclusions.

You have my condolences...Nintendo!

FOOLED YOU!