As far as character reveals, if we get a character, it will have to be a veteran that could be easily tied to the game. Like Luigi and Olimar, it is likely that it will say, "Want to know more about X? Visit the official website for ____".
So considering Pikachu is already revealed, I'd put my money on Pokémon Trainer, or Mewtwo. Lucario could also be there, but like I said, it will have to be a character that is central to the advertisements of each series and the specific installment. So I doubt we'll see Jigglypuff.
I'd like to see Wonder Red, as Wonder 101 looks like it will be great. But if he isn't revealed around the release of the game, i'm doubting his inclusion. For September, I think it's anyone's game. Although, I'd like to think it will be a character from a series not shown yet, veteran OR newcomer. So Fire Emblem, Mother, Yoshi, Wario, a retro character...etc...
Also, whoever thought of a Nintendo Direct that will encompass 2014 releases is a genius. It makes perfect sense that they would do that, and have another trailer for newcomers. I'm hoping we get more before then, but I would have to agree with that prediction.