I think if there is a new Fire Emblem rep, it'll almost certainly be one of Awakening's trio, or Anna, but she's definitely a dark horse candidate. The other options people have proposed, namely Roy and Lyn, simply don't make that much sense. Awakening was too important to the series. It's the one that saved it from cancellation, and it's also the best selling and most recent. That all comes into play from a business perspective. People are more likely to buy a game with a character they like/recently played as, and for the largest part of the FE fanbase, that's Awakening's trio. Out of those 4, I'd give Chrom 50%, Robin 40%, Lucina 9%, and Anna 1%.
Now, the question of whether FE will get a new rep is another question altogether. I like MA's guesstimate of 10 new total. That leaves us 6 more open slots, but not all series are at equal chances. DK and KI are both very likely to get new characters, so now we're at 4. Mario, I think is about done for reps this time around. Pokemon has maybe a 50/50 shot of getting a newcomer. Same with Metroid. So between those two, let's knock it down to 3. Zelda, Kirby, and Yoshi don't really have any reps that stand out for a need to be included. F-Zero, Mother, and Star Fox, I think, aren't really active enough to justify another newcomer, and as much as I love Mother, 2 reps is enough for a series that small. So, we've got 3 slots left, and the major series still left competing are Wario, Xenoblade, Punch-Out!, Fire Emblem, and maybe some other retro one. In theory, I think that leaves FE in a pretty good place. Maybe, at a 65% chance? I think FE's got a bit of an advantage due to becoming much more popular with Awakening.
So, mathematically, this ends up giving Robin a 26% chance of appearing. In terms of Fire Emblem, I wouldn't go for the attack myself, but if a character has a 26% chance to kill my guy, you can bet Basilio's sweet brown Feroxi arse I'd leave my guy out of range.
Again, this is all totally subjective. Maybe Sakurai will decide to add 6 more Star Fox characters. I dunno.