My greatest hope for seeing secret newcomers beyond the Gematsu leaked ones is perhaps the imbalance in the Pokemon character roster, the fact that there is a Fire Starter (Charizard) and the fact that there is a Water Starter (Greninja). Wouldn't it be awfully strange of them not to include a Grass Starter? And I don't see them just returning Ivysaur, as the rest present are all fully-evolved starters.
I don't want to act like the logic I presented above is the gospel truth, but it gives me real hope for further newcomers. A lot, actually. Unless Sakurai is just going to leave this flaw in the roster unchecked. I mean, I could be reading too much into it, but it makes Greninja's inclusion make a lot of sense if there is a Grass Starter waiting to be revealed.
I don't see it happening. I don't see why people believe so heavily in the "there must be starters of every type" thing from Pokemon. Sakurai flat out confirmed he picked Greninja because he liked the look of Greninja. It had NOTHING to do with filling the Pokemon roster with all three different types of starters. If anything we'll get Mewtwo and Jiggly back.
There are other valid things to bring up, though. Namely, lack of Villains and lack of Heavyweights on the roster. Villains tend to always be unlockable anyway, so it'd make sense for no villains announced pre-release. (Plus, in all honestly, the Ridley thing is blatantly obvious. He's too small for traditional Ridley and looks nothing like a boss at all.)
So yeah, I still think there's definitely plenty to go on. There's lots of Kremling love, as well, and DK had such a huge revival. Plus if we go by sales numbers (and we assume the only available source is at least SOMEWHAT accurate), Golden Sun is far more popular than Xenoblade, and even Dark Dawn sold just under the sales of Xenoblade. There's plenty of precedence for Isaac, and we're missing several AT's already, which could hint that another AT was promoted to playable.