This time, I don't think Sakurai will be hiding any newcomers from us. Of course, that's not to say that he won't make them unlockables.
I basically see it going one of two ways:
- Secret unlockables, Gematsu only knew the characters who were to be announced.
- All will be announced before, but Gematsu is incomplete.
I don't see how Sakurai would keep teasing fans with Ridley if he's not playable, he made no mistake about all the other deconfirmed characters; Ashley, Skull Kid, Waluigi, Dillon, Nabbit etc. Why tease such a huge portion of the fanbase only to disappoint them leading into the launch of the game? And I'm saying this as someone who has absolutely no fondness for the Ridley character, or the Metroid series at all.
I think the first scenario above is more likely, as we've always had secret/unlockable newcomers. I don't see why that'd change now.