the switch is to expensive to be liked by the handheld audience from the 3ds/ds/gameboy (often kids) and I dont see its gimmick gettting really popular in the casual market (like wii). Its still more or less a advanced wii u (you can take the tablet now far away from your console but thats basically it).
So imo we will look at the Nintendo home console customer base which is declining for generations now (Snes -> n64 -> gamecube -> Wii u).
The general interest in nintendo product just is declining. The Wii wasnt bought for the nintendo software or brand but for Wii Sports and the Wii balance board.
Something like paid online will definitly not help either.
I still do see the switch having a chance of an decent success:
If nintendo sells it as a iPad mini that can also play real console like games and nintendo games.
The price is compareable to and iPad/Android tablet, so as long as it can do what tablets can do (web surfing, netflix, amazon video, sky, facebook, youtube, instagram, photo editing, video editing, cloud storage like dropbox, calendar and such) I can see many people who are thinking about getting a tablet: "well, why not getting the switch, it does everything a ipad mini can do but im also able to play some mario / mario kart / zelda" and the price is the same/better.
That would be a huge selling point imo.