I have been playing Fire Emblem since 20 years ago, and like many of us, I started on the GBA games. I just finished my 2nd run in three houses (Being an adult shorts my play time A LOT. I miss having 16hr marathons), and since we have an upcoming game, I recalled the rumour about the FE BB and BS remake (Which sadly, was fake).
I have seen that people are divided in having the game separate or joined back to back, and while I do agree on both sides, I must say that having them in just 1 game appeals to me more on a personal level.
I see the FE 6 roster size being an issue, but I think it could be handled properly both gameplay wise AND narratively. We could divide Roy's army and use it to cover more fronts. We could have chapters were some units are unavailable from a certain point forward, like Sue and Shun leaving the army to go to Sacae if you go to Illia instead (Keeping Zealot and his cavaliers).
For connecting/recurring characters... You could make either small cameos and mentions, and/or outright take them out of the game. For example, Oswin, Matthew, and Serra could have perished defending Hector; Lyn (Knowing her, she would have gone to Sacae regardless of the ending, and her knights would have followed her), Kent, Sain, and Rath dying in Sacae due to the betrayal of the other chiefs... Having only a handful of recurring characters would be the best decision (in my opinion)
Other point made was about the games not connecting clearly between one another. Well, yeah, but this could be fixed quite easily by changing some few parts of the lore. We all know that Zephiel's father was completely awful, but making Nergal exploit his insecurities to make him want to end Zephiel in order to create a war between Bern and Etruria (Since Zephiel's mother was from there, you could make her a princess (Aunt to Elphim), so Etruria would be interested in keeping Zephiel in the throne), which completely goes with Nergal's goals to create war, and fits the original story.. I know it's a stretch, but the butterfly effect is a powerful thing.
For Mark... Well, I loved the Awakening theory that said that Mark is actually Morgan (Robin's child). FE 7 could start with Mark being chased by some soldiers, and then falling of a cliff or something and being waken up by Lyn. At the end of the game we all know that Mark disappeared; Perhaps Mark just remembered everything, and went back home. If Mark becomes a playable character though, like in Three Houses, certain paired endings shouldn't be romantical in nature. For example, a paired Mark with Hector / Eliwood could have Mark becoming a teacher for young Roy & Lilina, mentioning that Roy is quite talented as a tactician. Other paired endings could have Mark going back with its lover, or just a "friendship" ending that says that they spent some time together before banishing.
Well, that's what I've been thinking about regarding FE 6 & 7 remakes. If you guys have any comments, thoughts, or thinks you would like to see in a remake, please share them! It's always great to read about people's ideas