Here's my Idea for the Fire Emblem Reps: Lethe(cat form), Micaiah, Ike, Marth or Chrom, Mia.
Fire Emblem is one of the few First Party games represented in Smash Bros. Either replace Marth with Chrom, or don't do it. Having Chom replace Ike is a horrible idea, Chrom is a descendant of Marth, wields the same sword as Marth, and it would be Roy and Marth all over again.
If they add Marth, he should appear as he does in Awakening, Ike as he appears in Radiant Dawn, Same with the other RD characters. Add Micaiah, because she is a magic wielder, and also SSB4 needs more females. Lethe because she's a powerful Laguz. And Mia because she is a purple haired sword wielder. That's my opinion.