I'm not putting much stock in this, but there's a theory going on that 6 more characters could be added to both Wii U and 3DS and have a perfect rectangle and all that.
You know, Etika made a video about it with a click-bait title to boot. Same old stuff.
It got me thinking that, if we indeed get 6 more characters, that would mean a total of 10 DLC characters... It is a generous number, so to speak, but I could see it happen in one, and one only, condition: clones.
Yep, clone characters. Might include veterans like Pichu or Young Link or would-be newcomers like Dry Bowser, Blood Falcon, Dr. Luigi and other similar candidates to clone character additions. It's something that wouldn't be too farfetched and it's the kind of content that could be included in a patch for free similarly to the Miiverse and Duck Hunt stages on the Wii U and 3DS versions respectively.
Of course, this is just a thought I had. I don't believe we'll be getting that many characters. I only expect 3 or 4 more. That said, I wouldn't rule out the possibility that we may get more characters, even though some would be clones.