When it comes to newcomers, there isn't anyone that I'm absolutely expecting, but these four stand out to me:
Mewtwo: When it was initially revealed in it's new form, I immediately thought Mewtwo stood a chance, not to mention the movie going along with it. I thought that maybe his chances had been slightly less prominent after the feature of many "Mega Pokemon," but now that we know Mewtwo has TWO different Mega Forms, his uniqueness has been rekindled...again. It has a lot going for it.
Chrom: Despite what others may say, this totally follows what we saw in Ike's inclusion, to a T. This is a total opinion, but I really think Awakening completely stands out as a new Fire Emblem title; I'd be more surprised to NOT see Chrom.
Ridley: This is our only classic, recurring Nintendo bad guy left. Like Bowser and Ganon, he started on the NES and continues to be the recurring antagonist of his series. K. Rool, in comparison, came later, and now is not the antagonist we see in newer DK games (from what we've seen so far). When a new Metroid game comes out, you still expect that Ridley will be in it (in some ways, more than you expect Ganon to appear in a new Legend of Zelda).
Little Mac: This...is just my own most wanted character.