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.