So just for clarity sake, where are we finding the text "no unannounced fighters will be revealed"?
Reagrdless, I'm going to go with "I don't full trust the wording" camp on this one. Nintendo has said at multiple E3s that it's only going to focus on game releasing this year, but then drops Metroid Prime 4 announcements and whatnot. It's not that they are lying, per se, but I think they are misleading us so they can surprise us.
But let's be honest..there can't be that much of a surprise here. It's a 45 minute long direct. Even if Terry is more complicated than Ryu and Hero combined, it can't take more than 30 minutes to explain all of that (along with the stage and spirits). We have to be getting something else.