I would also note that I don't think Genealogy is the slam dunk a lot of people think it is. Do you do a SoV, where you leave the same maps? That didn't help SoV very much. Do you make them smaller? Then you've changed a fundamental part of the game. Yes, it has a support system, but uh, not in a way that people that liked 3H will necessarily like.
What about all the questionable stuff? Is modern IS *really* going to show the whole Deidre thing in its full HD glory? It's one thing when FE is a niche property in 16 bit or whatever. But is Nintendo really going to allow all the incest stuff, untouched, spelled out? I legitimately don't think they will. I think they'll be asked to change a lot of stuff.
Genealogy is an incredibly complicated game to modernise and port to a Nintendo console, and it doesn't exactly have the same things that made Awakening and 3H massive hits. This is why I think it's always around the next corner. I have no idea how they adapt it in a way that a. sells better than SoV, b. gets approved by Nintendo and c. keeps the game similar enough.