With the next Fire Emblem my next major Nintendo title of purchase without something horrible revealed, I was wondering what the title might learn from he last three modern F.E titles. 

Both from what they did right, and what they did not get right.

Well I hope you think the casual mode is one of the things they did right, because that's definitely here to stay in some form. Personally I'm pretty happy it exists because I appreciate the fandom beyond just the game and I love how much the fandom expanded thanks to it. Same goes for the "dating sim" elements. It's all coming back, and that's for the best as it keeps a huge part of the fandom coming back. I still play on classic because to me that's the only proper way to play, but I welcome the growth the fandom has seen from people who play differently. I hope they make better DLC, but I'm not getting my hopes up for that one.

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.

I hope they take the level design from Conquest, that was really great. Also the linear progression, makes the game feel tighter. That is about it to be honest.

From the first trailer it seems the third person exploration from Echoes will be back, which I hope it doesn't affect the level design like it did with Valentia. Also seems we have another avatar, so far seems is just choices, regardless I don't really like the avatars in FE, either they don't add anything or they aren't really avatars.

And personally I hope they stick to C-B-A supports, from my experience, the S conversations we got in Aw and Fates were...really questionable in writing, some reminding me of a really terrible videogame, but there were some really meaningful and great A supports between some characters, a chunk reminded me of some great convos in previous titles, specially from all the time I put into Fates, really I just want them to focus on that, is more satisfying than some quick trying to be romantic cringe it got.

I hope they learned to drop the child system if it doesn't make sense in the story. It def felt shoehorned into Fates and just felt awkward. I hope they don't have it in 3 House just for the sake of it.

I hope they will drop everything from Awakening and go back to a quality TRPG like Path of Radiance and Radiant Dawn (unlike Awakening where all the TRPG element took a nosedive quality wise). Don't care about the dating sim, there are lots of other games like that (and better ones). We lack a really good TRPG, it would be nice if they focused on this a bit.

And yes, I know I'm part of the minority about that, but I also know that I'm not alone