I think everyone here agrees that Chrom is the most likely character to join the roster.
I don't agree. In fact, I think Lucina is more likely than Chrom. I actually think the Avatar is likely also. Not sure if this has all been stated or noted here, but this is based on statements from the Developers and the relationship between Sakurai and Intelligent Systems.
-During a developer interview, the Nintendo director of Fire Emblem Awakening, Genki Yokota, stated that his favorite character was Lucina.
-In stated interview, he also mentioned that Lucina was one of the characters that made it from some of the very early concepts of the game.
-Lucina/"Marth" continues to top the character popularity polls among Fire Emblem fans in multiple regions (if not all, I'm not entirely sure).
-She was given that fan-service DLC Spa of Bonds thing for the most popular child characters (Yes, I know Chrom was in the parent one).
You may say, Oh, Yokota also stated that this was the first time being directly involved with the Fire Emblem series (he directed Xenoblade Chronicles, The Last Story, etc.), so maybe he doesn't have as much pull.. So maybe we won't get a decision from the Nintendo side, maybe it will come from the Intelligent Systems side.
The Intelligent Systems director for the game, Kouhei Maeda, stated that his favorite character story-line wise was the Avatar character. Important to note here is that Maeda also served as director for Fire Emblem: Fuuin no Tsurugi/Binding Blade.. which Roy is also the main character of. We all saw what happened in Melee.
So, based on the higher ups here, we might say that Chrom is not necessarily the most likely character. I'm not discounting anything that he has going for him (story-line importance, popularity, etc), but I'm saying that you can't necessarily call him the most likely because I don't believe that he is. It's up to Sakurai and Nintendo/Intelligent Systems to decide who he thinks is the best character. Given that Sakurai went to IS to get a character for Brawl and got Ike, I believe that we may end up with one of these two characters. That or we'll just go with the general developer favorite character of Tharja. Whatevs.
Here's the link to the interview:
http://fireemblem.nintendo.com/developer-interview/