Honestly I don't know much about the new Fire Emblem or who would be good in Smash, but I remember from the time right before it was announced that it was basically a game about Edelgard and potentially some other people. For the most part, there was one character in all of the marketing.
I would have liked to see more diversity in the FE cast, or especially some more non-character representation. They've got loads of great songs to spread across all of three stages, two of which are generic locations. At least they've got more than one Assist this round.
Back when Corrin came out, I was kind on board with Azura. Again, no idea of the game itself, but staff/waterbending seemed like a cool moveset. And of course I'm biased since there's another character in another series with that name...