Wii U: Chorus Men, Ridley, Dixie and Mewtwo.
3DS: DHD, Bowser Jr, Dark Pit, Dr Mario
They actually fit into the 3DS roster nicely.
http://i.imgur.com/PliZwku.png
and can support DLC nicely.
http://i.imgur.com/JajAywn.png
Next, none of the above newcomers have trailers revealed. Its possible none of these characters have trailers at all, as they are version exclusives.This would explain a lot in this sense.
Nintendo needs incentives to sell both games. They do this often, with games like Pokemon series. Having unlockable characters by owning both versions is one of the best ways to push both games. Especially when they need to push sales on the Wii U. It would actually make less sense to not include a feature like this from a marketing standpoint.
We have not seen trophies of either of the 4 Wii U characters yet. I know Karate Joe doesnt have a symbol, but the series symbols are overlayed behind the text, and this can be an easy fix with a future patch. For that matter, the polar bear does't have a symbol, yet many believe ICs are a strong candidate for DLC. If you belief they can be DLC, then you'd have to believe having no symbol now means nothing at the moment.
For this to be true, Gematsu would have to be true. Gematsu failed to account for the 3DS exclusive characters. Its very possible the leaker only had inside information with the Wii U version's marketing.
Then we have the /v/ leaker, who claimed these characters are in the game. Please refer to this thread for more details.
http://www.gamefaqs.com/boards/633202-super-smash-bros-for-wii-u/70028141
Lastly....if this is true, then this means the 4 characters above are indeed
in the games files. While 3DS hacking is difficult, it has been done, and I'd assume it wont be long before people start digging into the games coding. We won't have to wait long to know for sure.
This user claims his source is reliable
http://www.neogaf.com/forum/showthread.php?p=129524882#post129524882