I've written longer posts on it...but I really hope the next game uses established main characters like Echoes, rather than the psuedo-avatar character from Awakening and Fates. Romance is fine, great even, but I'd rather they focus on a few well written relationships rather than the whole "anyone can marry anyone" thing. More along the lines of Echoes and classic Fire Emblem. If 2nd generation characters return...for the love of Ashera make a good reason for them. No more Baby Dimensions please.
Past that, more fun challenging strategy gameplay, hopefully more along the lines of Fates: Conquest or the Radiant games. I don't mind if they have easy or super-easy or super-super-baby-easy mode...never felt the need to play gate-keeper on games I like. The more people that get to enjoy these games they better. I'd enjoy the Time Turner from Echoes again as well. It's nice to have that backup for when RNGesus hates you.
What will they carry over...hard to say, but I imagine the buffet-style DLC model will continue in some form. Just hope it's just one game this time...it took me 2 years to finish all the Fates playthroughs. I love Fire Emblem but these aren't the type of games I like to play consecutively.
NNID: Zephyr25 / PSN: Zephyr--25 / Switch: SW-4450-3680-7334