My problem with Chrom making it alone is that as far as fighting prowess goes, he is very generic. One look at Marth, and you can imagine he is more of a quick and nimble fighter. Ike's raw strength was a big deal in his games, and his Radiant Dawn appearance lets you know he is not one for subtleties. Now, what could Chrom do that is different from both Marth and Ike? Based on his design, I really don't know. Looking at the gameplay of FE:A though, pairing up is the big feature of the game, the first skill he starts with increases the chances of a character striking when paired up, and he doesn't want to shut up about bonds. Hmmm...
And as much as I would like Robin, I think his chances are slim to none. While it is arguable that Robin is the most important character in the story, he just isn't presented as such. Chrom and Lucina are the two most prominent characters on the boxart (Robin isn't even featured,) Chrom and Lucina appear in most of the game's cutscenes (you only barely see Robin during the first cutscene,) Chrom and Lucina are the two characters used to promote the game and its products like the soundtrack... Sure, most of that probably stems from Robin not having a definitive face, voice or even gender, but in the end, it makes it so Chrom and Lucina are much more the game's "face" than Robin.