So, there's been a new leak! It states that there will a Nintendo Direct on August 3rd, which will include an Iwata tribute and a reveal trailer for King K. Rool.
Here's a link to the images. The original leak was from 4chan, but it wasn't anything special. Apparently, all the OP said was that the Direct would happen on August 3rd. The images were the main course.
Personally, I do think that the inclusion of an Iwata tribute boosts the credibility of this leak. Furthermore, King K. Rool seems like a very likely choice for a DLC newcomer, given his immense popularity. The K. Rool model, however, does look a little low-quality. That's the main downer for me. It could, of course, be a similar situation to Mewtwo's reveal, where K. Rool is announced several months in advance to his official release, which would explain the lower quality, or they could be using K. Rool's in-game model, which would make little sense, but is a possibility nonetheless. That said, the render seen in the leak appears to be completely original, as no-one has found a similar model. That's another point in the leak's favor.
Personally, I'm going to take the stance that I always do. I'm going to remain skeptically neutral. There's only one thing against the leak, but it's a pretty big thing, and, while there are multiple possible explanations, I think it'll be better for me if I don't pick a side quite yet.