Sorry if this has been brought up countless times but I think a FE6+7 would really kick ass.
FE7 is the prologue, so chronologically this would make the most sense to be first.
( I don’t know if they would either include, exclude, or beef up Lyn’s story in the beginning. Maybe if it introduced the world of Elibe a bit more, but it’s kind of limited when it’s just the border of Sacae and some of Lycia. )
I would love a FE6+FE7 collab, but I can't tell if it would be too optimstic to expect a remake of 2 entire games for the price of one... but then again, they also brought Advace Wars 1+2 so who truly knows.
Elibe is pretty ripe for story telling I must say. For example the lands in FE13 aren’t very well defined. Just that the north is cold. Wow.
Duuude, one of my deepest wishes for a FE6 remake would be the inclusion of some sort of "Lilina Mode" like FE7 Hector Mode, not because I want Lilina to be a main lord (even though she's my favorite character and that would be nice to see), but since the Elibe games have probably my favorite worldbuilding out of the series (which Is saying a lot since Jugdral and Tellius are pretty good too), it would be awesome having two different "campaigns".
Roy mode would focus its cutscenes and story progression more towards the mysticism and lore involved with the Dragons and the Eight Legends and other stuff like that, meanwhile Lilina mode would focus more on the politics and the world of Elibe, how the nations are reacting towards the current war, if they ally or defy Bern, stuff like that. I even remember that the FE6 cast has a pretty diverse group of "political" leaders, like the Erturian Generals, Dayan being a chieftan of one of the main tribes, Juno being an ex leader of one Ilia's main mercenary squads, Yoder being a soon-to-be archbishop. So that easily could be fun thing to make about.
EDIT to avoid doubleposting:
I've always liked FE7 but every time I've replayed it I've come to love it more and more.
One aspect that I love about FE games is how they managed to make a 40+ hour campaign very replayable, I think I played FE6 way more times than I would like to share, and even then, every consequent playthrough is better than the last one.
Random stat level ups and 50+ characters definetly help, but I dunno, there's something so nice about getting better in a game with very simple options (Attack, Rescue, Item, Trade) or just trying to use a different strategy even if you're using the same characters from before.