I think Fire Emblem Awakening "Awakened" them to the idea (sorry for the bad pun). From what I understand it actually did pretty well. I got this info from Wikipedia though so I guess not 100% reliable though they do credit a source. "Additionally, in September 2012, six months after its Japanese release, Nintendo reported that 1.2 million units of downloadable content had been sold, bringing in an additional 380 million yen (about $4.8 million)"
As much as I love Fire Emblem Smash is a much, much larger series who's potential for DLC is huge. The best part of it all though is how Sakurai/Nintendo is going about it, they aren't "planning" any but are open to it. Nothing is being created only to be lazily detached and sold as DLC. If we get DLC it will be made after the fact, which is an awesome way to go. Especially because Smash is a game that could easily get away with day 1 DLC if it wanted to.
Err..sorry that was kinda super off topic but whatevs I guess.