When it comes to King K. Rool vs. Dixie Kong, I always saw Dixie Kong making it in over King K. Rool. If this were to happen, I wouldn't be too surprised if King K. Rool made it in as an Assist Trophy.
It'd suck, sure, but at least the character is in Smash in a form other than just a standard trophy. Krystal was my most wanted newcomer, and although it stings that she's only an Assist Trophy, I'm thrilled to see her as something more than a trophy in the first place.
Plus, there's always the chance that deconfirmed characters could make it as DLC. Pokken did it with Croagunk, so surely it could be done with Smash. And with how big of an outcry there was over Waluigi being deconfirmed, it could definitely be possible. Still not exactly likely, as it's never happened in Smash before, but I wouldn't say its impossible.