I really doubt they would release this huge amount of DLC. Nintendo isn't Capcom. Yet.
Nintendo's embracing DLC this gen and they've been riding it pretty hardcore. None of the usually scummy practices, but between NSLU, NSMB2, FE:A, and Pikmin 3 it's not really unreasonable to think they want a stream of content to keep SSB4 relevant for a while after release.
Obviously 15ish characters is pushing it, but we could see a lot in the works for SSB.