So in an [it's "http://www.gamevoices.co.uk/profiles/blogs/april-s-gamevoices-interview-is-with-the-extremely-entertaining-m]interview with Gamevoices[/url], VA/"mo-cap guy" Reuben Langdon mentioned that he played Raiden in Super Smash Bros.:
Since Raiden didn't appear at all in Brawl, nor has he ever been voiced by Langdon, many people took this as confirmation that Raiden would appear in some capacity in the upcoming Super Smash Bros. for Wii U/3DS.Later, Langdon claimed that he had mixed up Super Smash Bros. with Playstation All-Stars. However, many have noted this explanation is problematic, as Langdon has not previously voiced Raiden at all(not even in PSA), nor did he do mo-cap work for him in that game since Raiden's animations were ripped from MGR:R(and no, he didn't do mo-cap work for that game either).
Edit: I should note that Reuben Langdon has done voice work as Ken Masters and Dante (from Devil May Cry), so he's a notable name.
Also keep in mind that this isn't the first time something like this has happened: David Hayter revealed Jigglypuff's return fro Brawl, and Krystal's VA (Alesia Glidewell) leaked that Krystal would be appearing in Brawl.
Edit 2: Gamevoices has amended the interview:
I should also point out that it's possible that Langdon did uncredited mocap work for the cut scenes in PSA.