Almost guaranteed to be added:
Alm and/or Celica
Rex w/Pyra
Spring Man or Ribbon Girl
Decidueye
Highly likely:
FE 16 character or a popular FE character (Lyn for more female characters, Ephraim for lances gameplay, Hector for axes gameplay)
Bandanna Waddle Dee
Waluigi
Crash Bandicoot
Shovel...