On the subject of K. Rool, I think he has a fair chance. He's easily one of the most requested characters out there, and has a huge (and quite successful) movement to back him up, even despite his absence in recent years. Honestly, it says a lot about how much he's wanted when there's still massive demand for him after all these years. As far as possible choices for DLC go, he's one of the most ideal, and as such it would be silly for Sakurai to not at least consider him, and at that point, his credentials and potential as a unique addition to the roster could win Sakurai over.
Of course, he has his obstacles, like his absence from the DK series and his Mii costume, which Sakurai may see as reasons not to include him. Still, K. Rool remains one of the smarter choices for DLC, and I think we could see him added in the near future. He's by no means a shoo-in, but he's definitely one of the more noteworthy candidates.