I've seen several people talking about the likeliness of an online subscription service for the Switch, so I'm going to list the 2 main reasons I think why it isn't likely this will happen.
The majority of first party Nintendo games don't have online capability (Mario, Zelda, Pokemon for example)
A main selling point of the Switch is that it's portable, so a consumer looking to use the Switch on the go probably won't buy an online subscription.
I really don't think Nintendo will do this, but if it does I definitely won't pay for something as dumb as this.
Discussion started at here by alligator1779