Maybe I'm wrong, but it seems like most of the mirages are from the first Fire Emblem except Chrom and Tharja, which are from Awakening. There's this vast history of games, why just pick from those two? Seems like a huge waste
Virion, too.
This is what they said back in July:
Fire Emblem characters are being selected from Fire Emblem: Shadow Dragon and the Blade of Light and Fire Emblem: Awakening. Others will also appear as friends, or as enemies or masterminds.
Characters are selected based off things such as their popularity ranking data. Both Cain and Abel will also appear.
Characters that appeared as enemies in Fire Emblem will appear as enemies in this game.