Waaay too pessimistic for my taste.
Nintendo closing most of the services for DS and Wii wasn't their choice. As FAST6191 said, Gamspey's shutdown was the reason of this happening.
I'll also remember you this happened in, I think May, 2014. The Wii U launched in 2011. That's around 3 years of supporting something free when they could very well have stopped any support to the Wii to try to move people to the Wii U. Who knows how long they will support Wii U after the next console comes (Which hasn't been officially shown, people and media are getting ridiculous with this shit).
Capcom closing the servers for Monster Hunter Tri was in 2013, to give you an idea (And god, I miss those times. Thanks for Riivloution to been able to access online content).
About Super Mario Maker, I don't know. If you ask me; this seems the type of "game/application" that could easily be ported over the NX to continue it's life. It seems to have been pretty well received overall; and there is downloadable content on the way (Free, I think? Like Splatoon) so in theory they don't have any plans to forget SMM after release.
I don't see this thing been forgotten so soon.
There's also a BIG difference between past and now: Nintendo Network. That thing was created to last, unlike the online platforms of the Wii and DS, wich where pretty amateur and limited. That could make games with these capabilities last longer.
I understand perfectly that putting time into something that someday won't be be able to be shared or accessed sucks. I feel the same.
But then again, Why people play MMO's? They will close some day. Or have some kind of reset. Or even their servers can fuck up and lose information. Whatever happens, you end with nothing, as you can't play them offline and the data of all what you have is lost forever. That's the reason why I stopped playing them.
The same goes with games like Little Big Planet or games with editors in them. It's something that's going to happen no matter what (most of the times)... But I guess that the thing is to enjoy them while they last.
While I don't share your tone, I understand what you are saying. But this happens in other places and with many games just to focus on this one like it's the worst thing created by mankind, lol.
...Another option now that I think about it a little more, maybe, could be to create something like in Blast Works for the Wii, where there is a special online place where you can upload and share your things outside the Nintendo Wifi services if I recall correctly, called the Blast Works Depot.http://www.blastworksdepot.com/games/blastworks/
I don't know if it still works, though. I'll have to try it.
EDIT: Heck, who knows if in the future there will be a "Wii-U-mmfi"? I'm still amazed that people got to work online services for Wii so damn fast. I know it will be much harder but...