Ok so #1 We need Morgan and Noire in this game maybe a DLC where we can recruit them since they are canonically sisters.
#2 a dlc where you help the awakening gang defeat grima once again or in the last chapter of awakening.
#3 We need a bride class in FE Fates so yeah we need dlc for that.
#4 A dlc where you can save characters that died in the game and recruit them like Scarlet, Lilith, Mikoto, Asura mother Arete, Izana( nobody really cares about him), Garon maybe and Sumeragi.
#5 We need Tiki in this game not enough manaketes. I believe that is all for now.