Hours ago, Nintendo released some DLC they had promised just before E3, namely the Peach's Castle (64) and Hyrule Castle (64) stages. What was unexpected was a whole new round of Mii Fighter DLC costumes, one of which is free (K.K. Slider). King K. Rool, from the Donkey Kong series is officially released as both a head and suit costume for 75 cents.
The King K. Rool suit's significance is that he has been a requested character since Brawl, with a very similar popularity to Krystal. Now that he is being put in the game in the form of a Mii Fighter suit, that implies two things: Nintendo is still aware of long-time favorites, and King K. Rool's inclusion as a suit likely leaves open one more slot for Krystal as a fully-realized playable character. Of course, it could also mean that Krystal (and Wolf?) will show up as Mii Fighter suits, rather than new characters. No-one knows at this point, but I remain cautiously hopeful.