I haven't played any Bayonetta or Fire Emblem games so I don't have any emotional attachment to their series. So just looking at their appearance and style in sm4sh, I prefer Corrin at a glance.
Unlikely they'll be a new main since there's many other characters I love more, but you never know until you play them. After all, I wasn't expecting Charizard in Sm4sh to feel so natural to the point of feeling as comfortable with him as I do with Link (who I learned smash on). Perhaps the same could happen for Corrin and/or Bayonetta. As Charizard isn't one of those "MUST PLAY!" characters, I just merely like him a bunch.