Idea I've been sitting on for quite a long time. Exactly what the title says, it's a crossover between the 5 FE continuities: Archanea, Jugdral, Elibe, Magvel, and Tellius.
And how would you do this? :3c actually, most games only discuss a single continent, so there's no reason all games can't exist on the same planet at the same time. Except 4/5 6/7 and the new ones.
Outside materials written by the original creator of Fire Emblem actually state that 4/5 takes place about 1000 years before 1-3. My personal headcanon states that 6/7 takes place maybe 500 years after that, 8 at around the same time, and 9/10 800 years after that.
Yeah, but fuck that noise.
So, just say "They take place at the same time, deal with it."? That doesn't even work in the games' own private continuities.