I'd also like to keep the whole marriage and matchmaker aspect that we saw in awakening and fates out unless they figure out how to tastefully weave it into the storyline.

I think Genealogy of the Holy War best (and first) implemented the kids thing. There's a time skip, and your party in the second part of the game is composed of the kids of the first party (if they paired up) and new characters, too. I could gush on about FE4 when I have more time lol.

I'm thinking akin to how the Total War series handles army battles but making the choices of how to play each battle as being either classic turn-based tactical mode or going full musou hack'n'slash nonsense as options for gameplay.

My memory is hazy, but I think Divinity: Dragon Commander had something like this? A turn based strategy map, RTS battles, and you can activate your commander as a hero unit you directly control.

It's interesting that, at least to me, it seems like many people don't want a game with multiple strong aspects, either because they don't believe the developers can achieve it or because they don't like those aspects. I could see a Fire Emblem game with good story, good combat, and even romance/matchmaking for those who wish to seek it out. Though it would be interesting to see if they might take a Baldur's Gate style approach where you can roam around the world, talk to people, and have different kinds of interactions, with combat still being turn-based. This could be trickier with a whole grid and more units, but I think it could be done.