If you were a fan of what Nintendo and Omega Force's combined efforts were able to dream up with Hyrule Warriors (the Zelda and Dynasty Warriors hack and slash spin-off), then you're likely just as thrilled regarding the upcoming Fire Emblem Warriors. Intelligent Systems will be more lenient with the Fire Emblem IP than Nintendo proper was with Zelda, meaning we can expect series staples and familiarities to find their way to the Musou side of the equation. In theory, the partnership makes plenty of sense.
The upcoming Famitsu issue due out in Japan this week will feature new info on the game, and thanks to Japanese Nintendo's deciphering efforts, we now have a sense of which characters and content to reasonably expect. According to scans (higher resolution versions are supposedly on the way), the game is scheduled to release this Fall for both Nintendo 3DS and Switch, and is approximately 70% complete at the current time. Marth and Chrom have been confirmed as playable characters, as have a brand new sibling duo called Shion and Lian.
A preliminary look at the upcoming Famitsu. Full-resolution scans are, apparently, on the way.
The article goes on to talk source material, stating that Warriors will only pull from a specific pool of Fire Emblem titles: Shadow Dragon, Awakening, and Fates. Fire Emblem staples, such as the weapon triangle, the ability to promote and re-class units, and a character-switching mechanism, are all planned for the game as well. Finally, Mages and Archers are confirmed classes for the game, in addition to what I can only assume is a list of common and expected classes that will also make the cut.
If you're wondering about marriages or Warriors' potential as a "waifu simulator" (some people play Fire Emblem solely for that, you know), don't hold your breath; while friendships are confirmed, romance and subsequent marriages are not. As mentioned before, Fire Emblem Warriors is nearly complete and slated to arrive this Fall, so we should have the full Musou meets Fire Emblem story soon enough.